Painting Inside of Travel Trailer Bumper

coat a rag with motor oil... drag it back and forth a few times....

unless you built a new bumper from "L" channel and bolt it together after powder coating.. it will rust and damage the hoses..

You might try a small paint roller for trim with a wood handle. This one has a 2 inch roller.

You can also get paint scrapers that will screw onto the wood handles that might help with the loose rust and debris.

If the bumper is readily removable, it may be practical to pour a little paint in and slosh it around to coat. I don't know if that would be better than your idea or not.

I might be tempted to use a little sponge on the side of a stick, too, rather than a wad of rags; just seems it might be a little easier to control and waste less paint etc. If it's a long enough stick with the sponge in the middle, you could perhaps control it more easily by having two people cooperatively manipulating it, one on either end. Whether that would be easier or not depends somewhat on how well the two people can cooperate.

My bumper is 22 years old and has never been painted inside. I have stored the sewer hose in there since the 5th wheel was new. The trailer is stored outside 6 miles from the ocean and we often camp at the beach.

Small spots of rust does form on the outside of the bumper which I have to take care of every couple of years. None has eaten through from the inside or from the outside so far.

PVC roof gutter as insert or custom fit fence post.

I don't have any suggestions on how to paint the inside of the bumper tube so your idea sounds plausible to me. Why not?

But, I don't think you'll be completely happy. I quit using my bumper for the sewer hose years and years ago, because the rust causes sharp points, like miniature needles and inserting and pulling out the hose rubs across those bumps and sharp points, causing the hoses to get pin holes and small rips. Unless you can sand the metal down, even paint will stick to those sharp shards and can still puncture soft plastic hoses.

I use my bumper only for metal things now, like a fire poker, metal hotdog sticks, poles for my wind sock, pole for my RV brush, stuff like that.

My sewer hoses now go into a separate box with a lid. Lots of folks will add a sewer hose carrier under their camper frame or even attached on top of the bumper. They are made of PVC type square fence posts or 4 inch round PVC pipes. They are smooth on the inside, never get any sharp metal shards poking anything, and can be attached to the camper in a number of places, even across a trailer A-frame or under it, if there is space.

It's just food for thought and something to think about here as an alternative to painting that will probably still not keep sharp spikes inside the bumper from punching holes in your sewer hoses.

Unless you have it sand blasted on every section of the inside and coat it with powder-coat it, it will still rust but it will then flake the paint that you put on it off inside. I feel your pain, but to fix your problem, you can go buy a vinyl fence post and attach it under the trailer. There are threads on that.

None from me. Your plan seems good.