I'd forgo the towing of another vehicle until you have some miles on the new rig. Even if the costs of car rental are not absorbed somewhat by the fuel differential, the price is going to be worth the lack of worry and hassle with a toad.
You may also have to think about what type of hitch and wiring are needed, the particular toad you are going to have (not all can be towed four wheels down), and you'll have some idea with experience how your driving is going to affected by adding another 20' and 4K lbs. into the length and weight.
The suggestion to have some type of electronics for navigation and programs for RV related excursions is a good one. Common sense will be your best tool and not all are comfortable with electronics (rely on maps) but having some information about what's ahead, instantly, can be a great comfort.
Never visited a military campground but have heard they are a great deal and, if on base, should be very secure. You can also have a "Plan B" that would involve parking at a Walmart, a rest stop, or a close spot that looks secure. I like to do a good bit of driving at night because I can cover a lot of miles without traffic, sleeping passengers don't complain, and arrive at destinations close to daytime, when they can be most enjoyed.
I'm a tool guy (contractor) so I bring plenty along. Most of it goes unused. You'll definitely want things to cover tire repair, propane supply lines, and electrical. You'll probably also want common hand tools to tighten the occasional loose fastener or for need of disassembly/replacement. Plumbing tools can be a godsend when you're many miles from nowhere and you have a leak or the faucet breaks. A hand held multimeter and the knowledge of how to use it should be mandatory. Duct tape (I also carry Eternabond tape), mechanics wire, bungees, a fire extinguisher, small gauge wire, and road hazard markers (triangle reflectors) are things that I always have when traveling.
AFAIK, a call to your insurance agent is all that is needed before you pull off the dealer's lot. Make sure you do a "walk through" prior to signatures, testing all of the mechanical systems, alarms, and various fixtures. Look very closely for anything that would indicate a water leak. Leaks can be very problematic. Inspect the running gear and tire quality/age.
Good luck for your travels with the family. It can be some of the fondest of lifetime memories.
