I'm one of those folks who never left the driveway without knowing where we were staying, maps, budget for food, activities, misc. Yes, the DH has already told me I'm a bit OCD, the in the longrun he feels better as well. Neither of us like surprises. Suggest you make a preliminary plan, mapquest it, look online for camping facilities in the area and rough that in. Figure 10 mpg unless you're going to be in lots of hilly mountainous areas, then go with maybe 8. Are you going to eat all meals in the trailer? If not, base it on what you'd spend on average. I planned menus and figured the costs and plugged it in. After everything was said and done, for a month long trip, I'd add maybe $500 for misc and be happy if you bring it home.
Knowing where you're thinking of going will help get you some ballpark figures. We also tended to stay in State Parks. There are some Federal, but most often don't even have water to the site.
BTW, you're going to need to do laundry along the way, so plan on that. We generally tried to do no more than 300 miles a day, sometimes more like 250. Remember that it's a vacation, not a race. Allow yourself time to enjoy.