Did a 3 month trip several years ago. Spent a lot of time planning. First we looked at an overall route. Then selected what to see/visit where and how long. Also set some criteria for how many or few miles a day. Many times would find an interesting stop and decide that we would only travel x miles that day and spend the rest of the day sightseeing, of travel for a while and then sightsee and then travel some more. Looked up camping sites of PA parks, or KOA or other known places. Factored all this in and then when issues developed, and they did modified as necessary. Had some stops that were defining as to when and how long, as well as multi nights when we would do laundry, etc.
Its the nature of the beast and make the best of it.