Yesterday I finally applied two coats of POR-15 rust prevention paint, which, when done right, is just about the strongest anti-rust coating you can put on metal. I should have zero issues with rust whatsoever from here on out.
This has been a week of mostly awful work, crawling around on my gravel driveway under the trailer, smearing toxic chemicals on rusted metal 2" from my face. And while it doesn't look like much has been done, I'm going to sleep a lot better knowing that I just don't have to worry about the frame falling apart on me years down the road.
I wire brushed the plywood floor panels and coated them with boiled linseed oil to protect them from moisture and also from dry rot.
And the composting toilet is coming along nicely: