how to check for frame rot ?

[nickcrowhurst]

I've just carried out the spraying of the inside of the frame box sections with the rust-proofing fluid. To keep the spray nozzle in the center of the box frame I eventually settled on a piece of thin flexible plastic, cut from the lid of a Tupperware-type box. I cut a rectangle of plastic the same shape as the box section, so as to fit inside the box section with one eigth of an inch clearance round all four sides. I pierced a hole in the center of this, and slid the spray end of the 24 foot steel tube through the hole, so that about 4 inches of the end protruded. I slid a close fitting steel penny washer onto the tube on each side of the plastic, and located these tight up to the plastic with about ten turns of duct tape round the steel tube on the outside of each washer. It worked, and I made about 6 passes down each of the box sections. The flexible plastic negotiated some small obstructions in the frame, and enabled the tube to be withdrawn after the plastic had dropped out of the far end of the long sections. I fed the spray tube down the box sections, while my wife operated the spray gun lever when I asked. We did this for the two 22 foot frame lengths from the back end, and for the two shorter lengths forming the A-frame at the front of the trailer. After sorting out a damaged O-ring in the spray gun, the job went as planned.
One point worthy of note is that the trailer was filled with the fumes from the sprayed fluid, as the long box sections vent into the belly pan. We full-time in the trailer, so we were sleeping in the trailer the next night, and even with all windows open, the fumes were unpleasant. The next day, after the fluid had a chance to evaporate its solvent, I used the compressor to blow air down the box sections, and the fumes were gone.
On my trailer, the worrying corrosion of the frame is on the inside of the box sections, so for me this job was worth the time, thinking, energy and money it took to complete.
Nick.