Ending the Belly Pan Blues: Part 1
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Ending the Belly Pan Blues: Part 1
man using a flashlight to inspect the bottom of an RV
Getting into the area above the belly pan to service components is not for the faint of heart. Installing a zippered access panel makes it unnecessary to endure the pain of removing the belly pan.
By Bill Gehr / Photos by the author
I

f you own a trailer or fifth wheel, at some point you are going to need to gain access to the area above the underbelly — especially if you have one or more slideouts. You might need to service the dump valves, chase down a water leak or repair shorted wires; in my case, I wanted to dry-lube the rack-and-pinion mechanism for the slides, which required that I have access to the motor and gearbox.

Granted, it’s always possible to cut an access hole in the underbelly material and patch it later with tape, but that rarely works for more than a short period of time.

The solution is to cut-in a trap door — and you can find the right product for this purpose on Amazon. Normally referred to as a “trap flap” in the belly pan used for manufactured homes, the “Mobile Home Belly Bottom Repair Trap Flap” ($12.99) is a woven polyethylene, zippered access panel designed to adhere to the Coroplast or other underbelly material used on modern trailers; it’s 18 x 18 inches square and has a rounded flap that unzips to provide access through the underbelly.

Although slated for mobile homes, the underbelly materials are very similar (other than one is designed to handle road travel and the other is for stationary manufactured homes).

Coroplast or underbelly material has evolved from a basic plastic film to a modern honeycomb-type material with insulation glued to the inside. Unfortunately, these protective underlayment materials are universally installed in a single large section, which makes access much more complicated. Yes, you can cut holes, but putting them back to “whole” is virtually impossible. Cutting in a zippered panel saves hours of work when access is needed repeatedly — and damage to the underbelly material can usually be avoided.

In order to install the zippered access panel, you’ll have to drop the edge of the underbelly material at an estimated location that will give you a look-see of the component(s) needing service. For this project, the motor and gearbox assembly were in the vicinity of the rack-and-pinion slide mechanism that I needed to dry lube, so I had to decide whether to put the zippered panel in the middle or toward the motor and gearbox, which ultimately made the most sense for access to my targeted components.

At first I followed the installation instructions, but that was a joke. After determining the location for the installation, I removed the paper backing that protected the adhesive and stuck it on the underbelly material; five minutes later it fell down. Unfortunately, the wind caught the zippered panel as it was falling and it was ruined.

I decided to use a cardboard backing for the second try. The cardboard made it possible to handle the access panel material without losing control. Blue painter’s tape was used to keep the panel and cardboard together. I remembered that RV Enthusiast Publisher Bob Livingston had a problem with his access panel and he opted to use contact cement to keep it in place, which worked perfectly, so I decided to follow suit. I used a yellow construction crayon to mark the black, rough underbelly material at the location where the access panel would be finally installed.

The cardboard backing also made it easier to apply the contact cement with a 2-inch-wide disposable brush. Once the zippered panel was coated with contact cement, I applied the cement to the area outlined on the underbelly material. After the cement was dry to the touch, I started the installation of the cardboard-backed zippered panel at one end and lined it up with the horizontal marks that I drew around the cardboard. From the one edge, I slowly moved it into place without a hitch. Although the glue seemed to hold just fine, I applied some cheap duct tape that didn’t have a lot of holding power around the edge and let it set up for 48 hours. All the tape came off easily and the access panel was stuck securely to the underbelly material.

The next step was critical: The zipper was opened and a very sharp blade was used to cut between the zipper teeth and through the underbelly material. If you damage even one or two of the teeth, more than likely the zipper will not function. Contrary to the instructions, I opted not to remove the underbelly material under the access panel, which I felt would be easier on the zipper in the long run. To gain access I simply pull down from the rounded part of the underbelly material (without pulling on the zipper), and fold it out of the way when working in the area.

If you need a larger opening, you could always install a second zippered access panel next to the other one.

trap flap from Amazon
This “trap flap” from Amazon is 18 x 18 inches square and provides access through a zippered opening. The woven polyethylene material is very flimsy and can be difficult to handle, especially in the wind. Although it has a self-adhesive backing, I managed to destroy the first one and decided to use cardboard as a backing “plate.”
piece of cardboard with painter's tape around the edges
A piece of cardboard was cut slightly smaller than the actual size of the access panel and taped to the exterior side. This provided enough rigidity to handle without folding uncontrollably when installing. The cardboard was attached with painter’s tape.
hand using a construction crayon to make an outline
hand using a paint brush to apply a coat to a trap flap from Amazon
hand using a paint brush to apply a coat within an outlines area
A construction crayon was used to mark the outline of the cardboard-backed access panel. This little modification really helped with the installation. Hash marks were drawn for positioning.
After the first installation attempt of the access panel failed because the adhesive did not stick to the underbelly material for long, it was decided to use contact cement. The cement was applied with a 2-inch throwaway paint brush to the inside of the zippered panel and to the corresponding underbelly material, applying cement within the lines drawn earlier.
hand using a construction crayon to make an outline
A construction crayon was used to mark the outline of the cardboard-backed access panel. This little modification really helped with the installation. Hash marks were drawn for positioning.
hand using a paint brush to apply a coat to a trap flap from Amazon
hand using a paint brush to apply a coat within an outlines area
After the first installation attempt of the access panel failed because the adhesive did not stick to the underbelly material for long, it was decided to use contact cement. The cement was applied with a 2-inch throwaway paint brush to the inside of the zippered panel and to the corresponding underbelly material, applying cement within the lines drawn earlier.
hand using a blade to cut a zipper
hand pulling open a trap flap from Amazon
underbelly portion of a trap flap on the bottom of an RV
Once the contact cement dried, the trap flap was positioned within the marked lines. After smoothing out the material, the zipper was opened and the flap was cut between the teeth and through the underbelly following the contour of flap. You’ll need to go slow; if you cut the zipper, the access panel is toast. Normally, the flap is attached to the corresponding underbelly material with the self-adhesive glue, but in this case, it was decided keep the two flaps separated and flexible, which made opening and closing the zipper easier.
In use, the trap flap is unzipped and the underbelly panel can be hinged down to access the area. Of course, you can also elect to follow the directions and glue the zippered panel to the corresponding underbelly flap.
hand using a blade to cut a zipper
hand pulling open a trap flap from Amazon
Once the contact cement dried, the trap flap was positioned within the marked lines. After smoothing out the material, the zipper was opened and the flap was cut between the teeth and through the underbelly following the contour of flap. You’ll need to go slow; if you cut the zipper, the access panel is toast. Normally, the flap is attached to the corresponding underbelly material with the self-adhesive glue, but in this case, it was decided keep the two flaps separated and flexible, which made opening and closing the zipper easier.
underbelly portion of a trap flap on the bottom of an RV
In use, the trap flap is unzipped and the underbelly panel can be hinged down to access the area. Of course, you can also elect to follow the directions and glue the zippered panel to the corresponding underbelly flap.
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