65 and we want to rv

Sorry, Florida is closed to Canadians. LOL
If it opens you might do a search on this Forum in the RV Parks section for Florida. Then search the results for `snowbird' to minimize the posts.

Look here: Snowbirds

I take it you are eastern Canada Canadians.
Most boondocking opportunities in the states are out west.
But THIS LINK will be a good place to start looking for free or inexpensive campsites.
Although you are a little late you could look in the workkamping forum to see if there is an opportunity to exchange a little labor for a free or reduced rate campsite.

You will have lots of Canadian company! What do you want to do or see? How much do you want to spend (US)? These are questions you need to answer before choosing destinations. Do you want to be near a beach? If so, the costs are higher than if you just want a place out of the cold. Make reservations early! We moved each month. Monthly savings are significant. In some places, you may only reserve Februaryif you stay two or three months in one place. Most prefer the warmer climate roughly south of I4.

Not sure about the rules, but I believe there's a limit to how long you can stay in the US. Plenty of Canadians on the site would be able to answer. If there is a limit, that would alter your "full-time" plans. You may find it necessary to keep an S&B home in Canada.

How's your health?
You will most definitely need health insurance.

Get some quotes.
Start here and check other places
http://canamins.com/language/en/home/

My parents were RVers. They headed south in the winter. But for the warmth, not the ocean. They found some CGs along the west coast of Florida south of Orlando but about 5 to 10 miles east of the Gulf. Major price difference.

Not many boondocking places, in the high season even less. From Ocala south to the Orlando area you can find spots for less than $500 a month. These will be away from major metro areas and you will have to pay your own hydro (see I speak Canadian). You can also find upscale places that will be over $1000 a month, pays to shop around.

Our 1st year we picked a place in the middle and used it more as a base. We ran a lot (5,000 mi for 3 months). I know more back roads than some of the locals.

There are plenty of spots. In our area a couple of places close to each other that have 500 sites each.

Some people say it's not a problem in the deepest months of winter but my experience in dec and March in the gulf coast areas is being bit by noseeums. You may want to investigate it more. They are sometimes called flying teeth. Some people are not bothered and some are eating and miserable. I dont go near those areas at any time of year.

No free boondocking in FL. State parks have a stay limit of 14 days. Here are some examples of parks and their winter rates. We like Williston Crossings RV Resort in Williston FL. Nice amenities, beautiful grounds. Current rate back in $627 plus metered electric. Our electric bill was about $75 per month in the winter. Williston is located near Ocala FL. The winter will be cooler there than south of Orlando area but during most days it's still warm in the afternoons. Another park we like is Christmas RV Park in Christmas FL. About same price as Williston. To find cheaper parks you can check www.rvparkreviews.com and then look at their website for rates. Many of the cheaper parks do book up fast during the winter. The areas near the coast will be more expensive. Lots of people winter in Clermont and Arcadia areas.