1st, that's a bunch of miles for a vacation. I'd start with figuring out my goal. Is it to spend as much time as possible in CA or to enjoy a vacation and include your old hometown in that trip? If I have kids in tow, I'd opt for the latter. If it's the two of you wanting to maximize time in CA I'd fly.
As you have stated. everyone else wants vacation in June/July so book early. Some popular places like Yellowstone book faster.
If you look at the route from Columbus OH (just a guess) to Goleta CA (2,340 miles according to Bing I-70, I-44, I-40, I-15, etc... )and break it up into 400 mile days, that's 6 days out and 6 days back. 400 miles of pulling a trailer is probably 8 exhausting hours of driving. I trip plan at 50 mph in my big truck and it holds pretty close in the RV (cruise set at 60). Add packing up each morning, restroom breaks, lunch, fuel and setup each night, dinner, makes for 10 or 11 hour days. When we vacation, we have a 3 year old who loves to travel and 300 miles is about her daily limit. After 2-3 day of moving she's had enough. Slept all day in the truck, wants to stay up all night and play. I need sleep too. You get the picture.
Even without kid(s) 5 or 6 days on the road people want/need a break. Might even consider 2 days drive, sit a day, 2 days drive type rotation. In the big truck I'd give myself 4(600 mile) days to do this trip (limited mostly by log book/HOS laws). Actually with the new electronic logs it might take a little longer. Point is, do you want to drive more than a OTR trucker on your vacation?
Once you figure out how far each day, you start searching for campgrounds and there are several sources from Good Sam website to Passport America to Google searches. There are phone apps if you like them.
Return trip you can just use the same points on the way back or alter your route and swing a little north or south of your original route. Say you came back through Dallas, TX, your looking at 5,000 miles round trip.
For some perspective: 2,500 miles is an average week for an OTR truck driver. 5,000 miles in 3 weeks, vacation or work?
