Not really critical if the truck or trailer comes first but make sure you have an idea of what the other will be before buying the first (ie: if you buy a truck that can handle a 15k trailer, make sure you like the offerings under 15k before hand.)
As far as a full time site, are you talking at a commercial campground or on private land?
- Commercial campground: No big deal. Try one for a month and if you don't like it, hook up and find another.
- Private land: Check out the zoning laws first. Particularly in built up areas, many prohibit living in an RV. If you find land that allows it, go price up adding a driveway, sewer, water and electricity. It can get very expensive very quickly.
As you don't seem too experienced, I would suggest getting a less expensive used rig to try it out first without loans. New rigs take a big depreciation hit the minute you drive them off the lot. This gives you a chance to learn what you like or don't like with a much lower risk. Then in a year or two (or possibly never), you go buy a new rig knowing what you like or don't like.
If you aren't moving, Pianotuna has the right answer.