I have been along that route in my RV a few times, maybe not all on exactly old Route 66, but in the same area. Plenty of camping NOT a problem, Id buy the new for 2013 first time Trailer Life/Woodalls combined Campground Guide and maybe even the new Rand McNally RV specific GPS
If youre gonan do it in an RV Id suggest it NOT be in the summer as the arid southwest portion of the trip is too dern HOT that time of year, the next time I"m going to make it in either April or October, but if in the mountains of Colorado and Utah, that dont work then, high mountain roads are snow closed until mid June. We do alot of cheap and some dry (NO hookups) camping in places like BLM lands or US National Forest or Army Corps of Engineers campgrounds WHICH ARE FULL HOOKUP AND BEAUTIFUL AND MUCH CHEAPER THEN PRIVATE CAMPS.
Google all the RV Forums (like this site but RV and travel related topics) for a ton of good info on Route 66 in an RV
PS while not all on Route 66 if your in the West and come back the more central route (Utah) DO NOT MISS Grand Canyon,,,,,,and in Utah Bryce Canyon and Zion and Capitol Reef and Canyonlands and Arches National Parks we did all of those this summer.
PS if even more time, dont miss Glacier, Crater Lake, Mt Rainier, Yellowstone and Grand Tetons, we did those the last trip.
I LOVE the RV Lifestyle, headed South soon
2001 Four Winds 5000 29 Ft Class C Motorhome
454 Vortec Chevy w/4L80E Overdrive Tranny
110 Gallons fresh water storage capacity
86 Gallons gray water storage capacity
460 Amp hrs of (4) batterys energy storage
Soon to be added 200 watts of rooftop Solar
4 KW Onan Genset
My custom modified "Dry Camping Special"