I put a Winegard crank-up standard def dish on the roof of my four winds 18 last year. I didn't want to spend over a grand on an HD rooftop dish, and the standard definition image is just fine for what I watch. Direct charges me $15 a month for the standard definition box. A lot of people will recommend a portable dish, with the justification that if you park in the trees you can place the dish out where it has a clear view. There is merit to the argument, but I didn't want to lug around another piece of equipment.
Installation of the rooftop dish is easy and very straight forward. A caulking gun and full tube of Dikor will eliminate any potential leaks. I think the most difficult (if you can call it that) part was cutting the crank up hex shaft to the correct length for the thickness of my roof. Had the whole thing installed in less than 2 hours start to finish. Running the coax into the trailer and sealing up the passthrough took another hour. The instructions that come with the dish are very good.