The OR state campgrounds vary in how many sites can be reserved. Some are all, some none and some part. In May would not be to concerned and the parks are some of the best anywhere. We have found that if you get to them mid afternoon you can be pretty sure of getting in even in summer. Really like 2gysises route since it will take you through the Columbia River Gorge (my old home)on 84 which you should try to see if possible. Since you have a toad you could see Mt Hood and explore the water falls along the old highway. Our favorite parks in the gorge are Memaloose (part reservation) and Ainsworth (no reservations) see OR parks site for details. if you have time you could then take 26 over to Astoria for the Lewis and Clark Fort and Ft Stevens St Park is close by. Heading South down the coast is a good plan. Many great parks to chose from. You would have to cut over to see Crater Lake. Anyway you choose you should have a great trip.