My experience with the floor is that as long as you get it smooth, not glass smooth, but no bumps or lumps a good quality vynil will be fine. There is one issue to think about in a trailer though.......
The whole unit flexes and twists as you tow. If your single sheet flooring spans a seam in the plywood floor you may end up with a tear or crack. I know there are those that have done it and had great success, just being a bit pessimistic. The only issue I see with laying a sheet flooring down and then putting a 12X12 tile over it is that if there is ANY patter to the lower flooring it may end up telegraphing into the top surface over time.
I would get it smooth either with a basic sanding, fill the low spots and use the 12X12 tiles and be done. If you can lay a seam at the floor joint line so much the better. This is what I am planning on doing in my kitchen.