I currently have a DirecTV account at my home. I would like to get one for my travel trailer also. I've talked to a couple RV dealers and they will sell me a receiver and dish for anywhere from $600 t...
Whatever dish you get, standard def 18" or high def 36"... The most important part of setting up the dish is to make sure it is absolutely plumb. If you are off a few degrees on the ground, your off by a few hundred miles in space.
A quality tripod is a must especially with the larger HD dish. I recommend tv4rv.com. Their tripods are expensive but very worth it.