Everything in the FL market is handled by county. Check Google for some potential locations and then play with numbers. Property tax runs 10-20+% of assessed value per year.
You may not be able to get insurance on a trailer due to risk.
How will you finance the reminder of purchase price/closing costs after your anticipated down payment?
If you sell your UK property what ties will you use to prove your intend to return? Please do not rely on six months stays. The duration is up to the immigration official at point of entry.

From the moderator:

Taxes in Florida run about 2%, not 10 or 20%. I'm a Florida resident. I don't think there is any place in the US with tax rates much higher than 2.5%.

I'm adding this because even though I pointed the error out in a later post, the number seems to have stuck in people's minds.d