The truck: To tow a big 5er, DO NOT EVEN THINK ABOUT ANYTHING LESS THAN A 1-TON DUAL-REAR-WHEEL PICKUP! MINIMUM, you want an F-350, Chevy/GMC 3500, or Ram 3500. My choice is the Ram: by far the best diesel of the bunch (5.9 Cummins), rugged 6-speed manual tranny. For the REALLY big trailers, you will NEED an F-450 or 550 to be safe. In this case, get the diesel & 6-speed with 4.88 gears. In all cases, I suggest the 4-door crewcab.
The RV: For motorhomes, there are 3 basic types, the class A, B, & C.
Class A: These look like a box on wheels, & come in 2 major types: gas-powered front-engine models, & rear-engine (pusher) diesels. There are a few front-engine diesels, but not many. The front-engine models are cheaper, but tend to be VERY thirsty (<6MPG loaded), & some are very limited in carrying capacity, due to chassis capacity. The most common models are Ford-chassis with the 6.8 litre V-10 & 4R100 automatic, or Wokhorse-chassis with the General Motors 8.1 Litre gas V8 & 5-speed Allison automatic. Pushers are usually Freightliners, a few Spartans. Most (~95%) run Cummins diesel engines (many are the same as used in the Ram pickup), Allison automatics, & the larger ones have air brakes. They're slower off the line than the gassers, but get MUCH better mileage (~9-10MPG), last longer, & have more weight capacity.
Class B: Essentially, a conversion van set up as a camper. Probably not for you.
Class C: These have a van cab (99.9% of late-models are Ford Econoline E-450's) that ends just past the doors, with the RV body. They're MUCH cheaper than the A's, & seem to use floor space better. Biggest downside: almost all have gas engines (Ford V-10), & are gas hogs. A diesel class C would be a good choice, if you can find one. Beware of the bigger ones, especially with slides: many have little weight capacity.
There are also what I call "Super C's", which are medium-duty truck cabs & chassis (I've seen Freightliners, GMCs, & Internationals) set up as motorhomes. They're beautiful, but very spendy.
RV stuff:
http://irv2.com
Truck stuff:
www.thedieselstop.com