Open or closed frame tubes?

[Larwyn]

Why not just use channel or angle iron instead of tubing. That way there is no hollow channel to try to seal against moisture, and all the surfaces that should be coated and protected are on the outside where they are relatively easy to get to.

I'm sure there are a few hundred new trailers for sale within 50 miles of my house. Some were factory built, some come from small fabrication shops, I would doubt that I could find one with a frame made of tubing. Some might have pipe railings but the frames are channel or angle.

If I were to build a trailer using square tubing I would leave it open so that it could drain and air dry easily. It is not easy to exclude moisture from a closed tube, and even more difficult to get it out. When the temperature drops, a vacuum will form on the inside of the tube and suck moisture through any pinholes (even those on top of the tubing). The water is heavier than air so will settle on the bottom of the tube. Even though the vacuum will reverse as the temp rises, and the pressure will expel air out all of the same pinholes, much of the moisture will remain inside the tube.

Even though tubing is easy to build with, it just might not be the best choice for a trailer frame.

[cracker39]

I used 2x2 11 ga. tubular for the Squidget rails, and plan to use 2x3 14 ga. for the PT rails. I cut miter corners and my son-in-law, who did professional welding did the Squidget frame and will do the PT frame too. He does near perfect welds and I find it hard to think that his welds will have any leaks in them. I’ll probably use the oil trick this time. After the rear corners are tacked, I’ll raise the front of the side rails a foot or so and pout in a little oil in each side tube, then lower it and weld the front rail on. That is, if he thinks it’s a good idea since he’s the welder.

The tongue, and bumper parts all had caps welded on and we’ll do that again for the PT. Something I have thought about and wonder if it would work is spraying expanding insulation foam in each end of an open tube, letting it harden and trim off the end where it has pushed out. I’d think this would keep water out unless the foam would wick water through it. An epoxy coating on the foam surface might prevent that. Any thoughts on this crackpot idea?