The only tips I can tell you is that if it looks like it's not rusted through, doesn't mean it isn't close. The welder's way of looking at it is you only see about half of what's really rusted. We fixed up a trailer last summer that we picked up for about 150 - old King 2 horse trailer from the 60's. Kinda nostalgic. We ended up replacing nearly all of the supports in the floor, much of that in the walls, roof, and doors. Much more that it initially looked like needed to be done. You'll need to sand out all the rust - a power sander is a god-send for this - just keep going until you hit shiny metal. You'll then need to braze in some sheet metal if it ends up being a bigger hole than you anticipated, then sand out the seams to make it look level. In fact, just sand blasting the whole danged thing isn't a bad idea if you're going to paint it anyhow. We ended up doing that with ours, not just to make the paint look sharp, but to put a special primer on after the sanding that turns any remaining rust into a primer, and haults the rusting process. It can be expensive, but it's SO worth it. A great primer makes for a great paintjob. You can get automotive paint for your colors, but then you will have to clear coat it to protect the paint. For horse trailers, trailers, and other farm equipment, we get tractor paint. No clear coat needed, but we will do a few coats of clear most of the time anyhow. Without knowing exactly what's goin' on with the ramp, it's hard to try to throw out some help.
I'll try to see if we have a before of the trailer - I can snap an after anytime. ;)
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