We pull with a 2008 F250 crewcab 2wd 5.4 gasser with 3.73 rear. We go on 10+ weekend camping trips a season, usually within an hour or two of home. We went to Fort Wilderness in 2008 (4 months after buying the truck), and the truck was flawless.
With family, definitely get a crewcab -- the extended cab just doesn't have enough room, even if you think it does. The Ford superduty crewcabs are really big and roomy. The Dodge Megacab is great, but it cuts down on your bed size. I almost bought a megacab from a friend.
I average about 9 mpg towing our 21' TT, and just under 16mph empty on the highway.
I had a 2000 7.3 F250 previously, and honestly just got tired of the diesel. Although diesel is a lot more common these days, every once in awhile I would get caught running low and having to pass a lot of gas stations looking for diesel. I found maintenance costs to be a lot more expensive. The engine may very well last for 500,000 miles, but it better after spending so much money on it. 4 gallon (not quart!) oil changes of more expensive oil, replacing fuel filters (when was the last time you had to replace a fuel filter on a gasser?), draining water from the fuel filter (I had never heard of this before), being paranoid about the antifreeze/coolant (not just anything, but whatever is the most expensive at the parts store, if they have it), plugging in the engine block heater in the winter, waiting for it to warm up in the winter (neighbors love that), waiting five minutes at idle for the engine to cool down after driving (or you can cook the turbo), and more. And now diesel is averaging 40cents more a gallon than regular gas at the pumps in my area.
I got about 12-13mpg towing with it, and almost 21mpg empty on the highway.
I did like the truck, but just got tired of it. Doing just one or two long trips a year, that is hard to justify a diesel, especially at ~$8,000 more than a gas engine.
A friend bought a used Chevy with the Duramax. It is a great engine, very smooth, and REALLY quiet for a diesel! That is the best way to do it, I think -- if you really want a diesel, and don't have an unlimited budget, take your time to find a good used one.
Otherwise, buy a F350 Crewcab King Ranch! Yea Baby!