The antenna on the roof of your trailer will work perfectly fine for any television you may have, unless it's an older one. You will get "over the air" programming and it will all be digital, and the antenna will do just fine. Any television you purchase NEW TODAY will be ready to go. Just hook up your coax cable from the jack in the trailer to the connection on the television and set the television to search for the stations.
Yes, every location you travel to outside your current spot, you'll have re-scan for the stations. Yes, if you turn the antenna slightly, you may get some channels and some you may not.
A simple tip when you are pulling into a new campground, is to notice the other campers that are set up and look at the roof of their trailers. See what direction the majority have their antennas facing. This will give you a rough idea what direction to start yours off with when you first crank it up and then scan for your stations. You may need to turn the antenna slightly if you get pixel freeze, and some stations may come in at different times of the day depending upon signal strength.
I WOULD NOT change anything on your new camper until you have at least use it for a while. I've had 3 travel trailers and the oriignal install antenna has worked perfectly fine for us. We also have DISH satellite, but we always watch local stations over the air too, no matter where we are. There are some stations over-the-air you simply cannot get on cable or satellite (like ME-TV).
Don't change anything. Get a new television, hook up and go! If you are THEN disapointed .... THEN consider making changes!
Good luck! Congrats on the new camper!
EDIT: You do not need to jack up the camper to get the tires off the ground. You run the risk of bending the frame, and trailers are designed to sit on the wheels. The jacks on your camper are use for stablizing, not lifting. Just snug them up so the camper does not bounce up and down on the springs. That's their intended purpose. If you are permanently parking the camper and it will never move, then you need to get proper supports under the frame, then you remove the tires, like a mobile home. Otherwise, no!