If you've never done it, squares is easier. But I don't like the self sticking ones.
You can skim the floor with a watered down "thinset." Tile stores or Home Depot will have it. Mix it so it's thin enough to slide completely off a trowel. Skim the floor and it'll fill in any cracks or grooves. Remember, your goal is just skimming. Not coating. Lightly sand it afterwards to remove ridges. Vacuum and sweep. Get all dust off.
Then use the vinyl tile glue with a small notch trowel and do small sections at a time.
The most important thing is to figure out your layout first. Don't just start in a corner. You'll end up with small odd cuts that way. Figure it out so that the cuts even out on each side the best you can. With all the corners in a TT, that won't be perfect.
That's one way.
The single sheet method is better, but much harder if you've never done it. I'll try to explain.
Skimming the floor is the same. Glue is the same.
First thing you want to do is remove everything you can that's not bolted down. If it is, and you can remove it and find the holes later to cut through the vinyl, then that's better.
Then lay down construction paper (usually in the paint section of the store) and cover the whole floor. Tape all the paper together so it can be removed in one piece. This is your template. You may find it easier to do large sections of the trailer separately depending on layout, but that'll cause seams in the floor.
Once you have your template, lay it over the new vinyl and tape it down here and there. Just so you can work on it without it moving. Then use a cutting tool (they make rolling razor cutters for this, but a box cutter works too) and cut out your piece of vinyl.
Then you need to check that it works. Lots of people cut the vinyl backwards, so watch that. Once you know it fits right, spread your glue on the floor in manageable sections starting in the back.
If you roll the floor up it'll be easier to carry into the trailer to start laying it. Don't spread more glue than you can reach across. Two people makes this so much easier in a house, but a trailer will be cramped.
Start laying the floor and spreading more glue as needed.
I hope that made sense. It's really hard to teach that in one post. There are youtube videos on it. This is a big job. Most trailers have a floor laid before furniture is put in. That furniture is going to be your obstacle. That's why sections or, better yet, squares will be easier.
It can be done fairly cheaply. I just hate the self sticking type. They peel often leaving you with a worse floor.
I've done it. In two days. Day one: cut out old floor and skimmed it. Let dry overnight. Day two, figured out my layout, spread glue in small sectiins, laid tiles. Done. That's really what I'd recommend for someone who's never done it.
Whatever you do, don't lay new vinyl over old. Just won't work out.
Hope this helps. Feel free to message me for clarification. I used to be a tile setter and did an awful lot of vinyl too.
