Look at the listed "dry weight" of the RV. You will probably add about 1000 lb to that if you travel light and 1500 if you take tons of stuff. You will have clothes, food, bedding, etc. Also, the dry weight doesn't usually include propane tanks and battery. Pick 1200 lb as a number added to the dry weight.
10-15% of the loaded weight of the trailer has to be transferred to the tongue and thus the hitch. This becomes part of the cargo of your trailer. So pick 12% for a good intermediate number.
Calculate 12% of the loaded weight. Add about 60 lb for the weight of a good sway control/weight distribution hitch system. Add that to the weight of the passengers, their stuff, and whatever else will be in the truck. All that is the cargo weight of the truck. Add the curb weight of the truck, and see if you are over the gross weight (not combined weight) of the truck. Quite often, cargo weight is the limiting factor on a 1/2 ton truck.
My advice is to buy a lighter, cheaper, smaller RV for a starter unit. Find a used one if you can. Quite often people sell them in the fall on Craigslist. Keep it at least until you are ready to trade up in truck. Then trade the truck up for something that will comfortably tow the RV you want.