Jerry,
You'll get alot of differing opinions on this I'm sure but here is my .02 cents. Looking at your towing situation I would think getting a diesel isn't going to be a neccessity. Especially with the newer model trucks which are pushing 10,000 or more lbs of towing capacities. I would think you'll be alright but I wouldn't expect to break any speed records.
You should also expect to that wear and tear may be a little more evident in terms of brakes and suspension parts than normal. Just be careful that you look at your total loaded weight or GCVWR and you don't go over that. So that 4 hour trip if you've loaded down the bed and got all your goodies you might be ok on towing weight but what about total weight of the truck and boat combined. Just something to think about.
Can't give you any feedback on an F-150 because I'm towing my 236LS with a F250 and forget it's even behind me!
But in short, I think you'd be fine with any of the newer model 1/2 ton pickups.