We knew that we wanted to fulltime for at least 15 years before we did so I don't think that you're planning too far ahead. Read as many fulltimers blogs as you can -
http://www.hitchitch.com/links.html. Each fulltime lifestyle is unique but you'll get an idea of what you might like to do and see, how much you'll want to travel, where you might want to stay. It sounds like you'll be snowbirds without a permanent house in the north but a you'll still be returning north each year to the same region. There are fulltimers who do just that.
We started fulltiming over 20 years ago and I really don't think much has changed. The internet and cell phones have made everything easier. Gas is a lot more expensive. Campgrounds have gone up in price but overall not as much as other things. More people are camping so parks are busier.
DutchmenSport's advice is excellent.
Answers to some of your questions:
MagillaGorilla wrote:
Someday in the distant future (15-20 years) the wife and I think we want to go full time in a MH.
We have a few questions for the full times out there.
How often do you travel? We're unusual because we travel to lot, about 15,000 miles a year and we travel slowly, maybe 50 - 100 miles at a time.
How long do you tend to stay put? We stay from a day to a week, rarely more than two weeks.
How do you get your mail? We use a friend's house as our mailing address. They forward our mail to us about 4 times a year..
How do you acquire a campsite for months on end? We don't.
What does a site cost per month? We boondock a lot and stay at public campgrounds so it's very inexpensive.
What are the things you miss about having a brink and mortar house? Nothing.
What advice do you have for a person thinking about becoming a full timer? Don't wait until you're old. If possible retire young or at least cut down on the hours that you work. Enjoy life!