Need advice about a truck and camping trailer combination

How many people do you need to sleep because there are plenty of trailers servicing your other needs in the sub 20' range that you can pull just fine with a F150. Especially if you step up to the 4.6 over the 4.2 or best the 5.4. It's a complicated matrix of engine size, drive train layout, body style and wheel base but you can see http://www.fordf150.net/2007/2007-ford-f150-specifications.php that towing capabilities on say a 2007 F150 can range from 2300lbs to 10,500 lbs with the 4.6 bottoming out at 6000lbs. Now if you want to pull a huge 30' trailer or some massive 5th wheel you'll want to step up to a larger truck but 6000lb loaded is a lot of trailer.

Turning and stopping with a trailer is where people get in trouble. This cannot be over-emphasized. You will be able to tow with a smaller rig and it will last a lot longer as well as be safer if you are a good tow driver so consider a class in towing before heading out. Having said that most campers are pretty light unless you're talking about a huge fifth wheel or something that has two bedrooms.

I only need to sleep 3-4 people and 2 dogs. :)

You can pull a pop-up with a 1/2 ton; heck, my Subaru can pull a pop-up. You'll probably be looking at an F-150 in your price range; they're plentiful and Tundras tend to hold more resale value. Be forewarned that this is a tough time to buy used. Prices on used vehicles are high right now, and looking for a high-demand vehicle (aka a truck in Colorado) can't help things in that department. You'll want to get a V-8. While gas is a killer right now, you can actually even out a lot of that in Colorado. My sister (lives near Cortez) does about as well fuel-wise with her GMC 1/2 ton V-8 as she does with her V-6 vehicles. This is because she doesn't have to put as much foot into it to maintain highway speeds on the grades she drives on every day. Keep in mind, though, that no matter what you do, gas will kill you in a truck. $3+ per gallon is likely here to stay. Commuting in a vehicle that costs you $100 a week to put gas in gets old quick.

I only need to sleep 3-4 people and 2 dogs. :) When you are figuring out tow ratings and truck capacities, don't forget to add in the weight of those four people and two dogs. A lot of half-ton trucks don't have enormous cargo capacities. Four people at 200 pounds each, plus two big dogs, some firewood, and a couple coolers of beer can put you close to your maximum capacity even before you add in the tongue weight of the trailer. As someone who has owned both half-ton and 3/4 ton trucks (as well as a couple smaller ones along the way), I'd say that the difference comes down cost, comfort, and capacity. The heavy duty truck will cost you more to run -- more expensive to buy, more gas, bigger repair bills (because the parts are bigger and cost more), more expensive tires, etc. The half ton will be far more comfortable (and safer, because it handles better) to drive unloaded, which for most people is about 99.99 percent of the miles they drive; a heavy duty truck will beat you up every time you hit a bump in the road. But if you are going to be carrying or pulling heavy loads frequently, you need the heavy duty truck or one of the new half tons with tow ratings close to the bigger trucks. It's safer for you and everyone else on the road. It's not so much about bigger engines as it is about brakes, suspension, and a chassis made for huge loads. The rules vary by state, but if the trailer is at all heavy you'll want trailer brakes, which of course adds cost -- more expensive trailer, and of course you'll need a brake controller installed in the truck. From a safety standpoint, I don't think it's a good idea to be maxing out your tow or cargo capacities routinely. If your trailer is going to weigh 5000 pounds wet, don't buy a truck with a 5500 pound tow rating; it's far safer to be in the middle third of the capacities. tl;dr: Go trailer shopping first, decide what will work for you, and then buy the truck that will work for the trailer you plan to buy.