DO NOT USE RUSTOLEUM. Both grades of their bed liner are absolute junk. They peel and dissolve with any solvent (delim), creating tar that sticks to everything.
I painted plywood a few days ago with Seal Krete Epoxy-Seal. It's intended for concrete garage floors, but should work well on sealed wood. Supposed to be three times tougher than floor paint. You can add non-skid sand, but I don't want to sand my equipment.
I also did a van floor with Duplacolor bed liner. Not very durable.
I would paint walls and floor of that trailer with multiple coats of epoxy. Seal Krete comes in gray and tintable white. Thirty-some bux/gal at Lowes.