Look closely at the TV capabilities as others have suggested. Verify the TV will be able to handle your rig up hills and down hills. You only want to buy a TV once.
The rear axle ratio makes a big difference in the GCWR too. Don't let the RV sales rep tell you "sure your truck will tow this rig" as they are primarily (I hesitate to say only) interested in selling the camper.
I agree you'll need a dually for the pin weight.
TV mileage will vary. Your driving habits will have the largest impact on mileage. My other truck (06 SRW 5.9 all else the same) got 11-13 MPG towing and 18-23 empty.