Can someone help me with 5th wheeler info please?
Yes, the tow vehicle and the trailer are almost always sold separately by dealers, but must be matched to be safe and effective. It is rare, but you may find a private party selling the combination (used).
The 'little truck', known as a 'pickup truck' is available in 5 'weights': Mini-truck (not suitable for towing), 1/2 Ton (good for towing very light weights only, generally to be avoided), 3/4 Ton and 1 Ton. For the biggest/heaviest trailers, there are 'big trucks' available, but this would seem to be overkill for an 'extended vacation'.
For the most comfort and conveniance, go for an 'extended cab' or '4 door' model. For the best towing, get a 'long bed' model. Dual rear wheels and/or 4 wheel drive are consistantly debated as to whether they are necessary or not. In order to be able to get up hills easily, a diesel engine seems to be the best choice, but more expensive. Big gas engines (like the GMC 454 engine) can do the job well, but often use a lot of gas. Smaller gas engines, like the new GMC 6L engine, do well on flat land, but struggle getting up hills.
A 3/4 ton or 1 ton pickup will probably cost between $20,000 and $50,000 for new or a good, late model used one. Before choosing a truck, decide on the trailer first, as that will dictate which truck to get.
A light-weight, 25' trailer may be towable even by a 1/2 ton truck, and could be adequate for 2 people for a month or perhaps 2. Light-weight implies flimsy, so these may not hold up well. Heavier weight will probably last longer, and perhaps be more comfortable, but will require a bigger truck and more fuel to move. A longer length will probably be more comfortable, but much heavier.
Whatever length trailer you get, go for at least 1 slide-out; it greatly improves the livibility of whatever space you have. Trailers should run from $10,000 for a short, late model used one to over $100,000.