I have DirecTV, with a Winegard 'Carryout' mounted on my roof ladder. More cost-effective than a permanent roof-mounted, and travels just fine.
One issue is that many satellites are at least a 2-line feed, and RVs--at least in this price-point, have just a single SAT-input jack. Unless one wants to fork over the $100, or so, for a SWM-switch, one must figure out a way to route that 2nd input......unless one doesn't have the need to either watch 2 TVs simultaneously, or the desire to ever record 1 show, whilst watching another.
As for cable?....I use it when a park I'm in has it, just for the local channels, and there is usually a separate input for it (on newer RVs), since RV mfgs have finally wised up to the fact that SAT & cable coax are different.
Now, there are a coupla' ways to get locals on DirecTV, and they relate to whether you're just a weekend warrior, or more of a full-timer. Intermittent campers are probably using the receiver from their home (although it IS possible to buy another one for your RV, and sign a 'nomad' certificate w/ DirecTV, and get the big networks broadcast from either LA, or NY....but it's costly, and somewhat defeats the purpose of 'local' channels), and wouldn't want to change their service address. Full-timers, on the other hand....especially if they only move 2-3 times a year (think snowbirds) can get around that by having DirecTV change their 'service address' to their current location......but doing that on any regular basis would not only be a hassle, but (I'm guessing that) sooner, or later, DirecTV would just make one do the 'nomad' thing.
The other thing....if one happens to camp only around metro areas, is that signals through the air are vastly improved, thanks to the change to digital, a few yrs ago. From a cost-effective perspective, if I went out only a few times a year, and only to metro-area RV parks (and wasn't an absolute TV addict), I'd be content with the roof-mounted antenna. I still use my antenna for local channels when I'm in a metro-area park that doesn't have cable.....and use a simple, Radio-Shack A-B switch to toggle between DirecTV and the local channels.
As for the issue of streaming video......well, it's (largely) ahead of it's time, relative to RV parks. It theoretically works, but the real-life issue is the poor quality/reliability of 99.4% of RV parks....they're barely able to support email. Paying for a Hulu flick, then getting pixelated garbage intermittently gets old very quickly.
