I am a genius at finding great little hotels for road trips when I plan ahead and a complete disaster doing it on the fly. Every time we tried to just find a place without reservations we ended up in a terrible place and sometimes were grateful to have found it. We had one trip where we were afraid we might end up sleeping in our car as we were turned away from half a dozen places on my list before we finally found a very dubious place with room. Our room was like a prison cell with a poured concrete bed platform with a foam mattress on it. It did have a very good restaurant. And we were not traveling in peak tourist season in July.
If you plan to do this, you should have a list of possible places and phone a day or two ahead as you go to reserve. You will be lucky to find openings, so have a long list.
I would identify some anchor spots along the way and plan two or three night stops to use as bases for the area. That way you also don't risk theft of your stuff at stops along the way as you can stow it at the hotel and then explore from there.
