I am doing exactly what the OP wants to do. I've been living in my RV (29' 5th wheel trailer) for 6 months, and I'm typing this post over my satellite connection from the northern Cascade mountains in Washington. Here is what I have learned:
1) Satellite is the only way to go when you get out in the boonies. When we started this trip, I had an Openmoko phone as a backup ISP, but I dropped the data plan 2 months later because I almost never had connection.
2) Hughesnet is the only affordable satellite provider. Some other companies resell Hughesnet service. I use Motosat, which caters to the RV market. You will probably have to use a reseller, as Hughesnet's own TOS doesn't allow mobile use and they don't want you as their customer.
3) You can get an ordinary residential Hughesnet dish and mount it on a tripod, but aiming that dish is a royal PITA. www.maxwellsatellite.com sells dish, tripod, and pointing gear as a combo for IIRC $500. But it's still a PITA to point (the record holder from their user's group did it in 5 minutes), and vulnerable to theft. I wouldn't consider it an option if you are going to be moving frequently. A better setup is a roof mounted tracker, like what Motosat makes. Their motorized, and usually acquire the satellite in under 5 minutes with no help from the user. But you're going to have to pay: new systems cost $5k. I got mine used off eBay and installed it myself for $2k. Soldering Iron not required, but expect to cut and crimp a little cable, and of course you have to do the roof mounting. The hardest part was lifting the dish up onto the roof, because it's 80lbs with mount.
4) Contrary to what some other poster said, these dishes are NOT comparable size to TV dishes. They are larger, because they need to transmit info back to the bird. They start at 0.74m diameter. This means that pointing them is harder than pointing a TV dish, and they absolutely cannot be used while in motion.
5) Do not buy an RV with a rubber roof. Just don't.
6) Are you using solar power? I do, and it's worked out quite well. I could give you some tips if you want.
My recommendation would be Hughesnet with a motorized tracker, and a 3G phone if you need connection while moving on the highways. You can learn more about my experiences with the technomadic lifestyle at http://lauralan.livejournal.com/