If you RV more than camp, then a 2wd truck will be fine in any RV resort. If you camp, taking your setup into unimproved roads with mud or loose sand will require 4wd or patience and plenty of traction material you will need to haul with you.
I agree you need a crew cab to fit your family and a dually to handle future desires of towing a large fifth wheel. You may want to check out the chassis cab trucks Ford F550 and Ram 5500 - I found some are equally or closely priced to the F350 DRW and 3500 with much more payload capacity.