We winter in the Keys every year and love it since we are kayakers.
Do not go to the Keys around any holidays!
Route 1, (the overseas highway) which is the only road from Key Largo to Key west is bumper to bumper during that time and Easter time.
Just after the past Christmas and New years it was stop and go for thirty miles.
If you are content to stay in your RV park or state park during those periods you will be fine.
The rest of the winter is great except it might be fairly crowded on the weekends when the people from Miami head here.
This is a fishermens and boaters paradise!
Jack L