You'll need the drill, the bristled head (Iwould recommend two since they're likely to gum up), a solid gallon maybe two of acetone, a plastic dropcloth of some kind, and two gallon cans of that stuff. I would use a heavy nap roller from home depot rather than the foam ones they give you. This will pull the texture up higher than the foam and allow for more traction when standing on a misty trailer unhooking your bike.
One coat won't be enough, it will be thin where the roller raises the texture, and may be thin enough for moisture to be an issue. Two coats are better, three is the shicken.
1) Strip the old paint off as much as possible with the drill and bristled heads. This is by far the hardest and longest step.
2) Brush the dust and loose dirt off with a broom
3) Use an old paintbrush and liberally apply the acetone. There is no such thing as too much, until there's a puddle under the trailer. Do this in the garage with a plastic tarp under the trailer to keep it from ruining anything it may touch (dropcloths are cool, too.)Take care for ventilation or you'll be in bad shape.
4) Apply the first coat of cover in the garage to prevent moisture from getting at it in the event of rain. Wait a little longer than the recommended cure times to ensure it's down hard.
5) Use air compressor or broom to remove any loose dirt that accumulated since the coat.
6) Apply next coat. Repeat to desired thickness.
Doing that, in my experience, was just as effective for my pickup as the spray in stuff costing way more. Plus you get to learn a new skill.