William, most people forget to treat the underside of their enclosed trailers. and it will rot from outside in too. bed liner works best for any trailers undercarrage
I agree, the bottom of the trailer should be coated or painted also, a lot of trailers I have seen, including mine did not have any paint or barely any at all. My new trailer will be painted on the bottom also to help it last longer.
Nice trailer William. There is a paint called POR15. I painted my trailer with it last year and it has been holding up great. It seals the rust in and once it dries you can't get it off. It seams to hold up against the chemicals pretty well.