I feel your pain, I planned our first RV trip and it was just husband and I. I made reservations at places that I figured I would need reservations and played it by ear. Half way thru our trip, we got some bad gas in NV which caused the engine to stall, but we didn't know what was causing the problem. Took it to a mechanic, he worked on it, and couln't find much. 5 hours. Drove it to the next place,stalled again and took it in to another mechanic Now we are a day behind and my reservations are all messed up. Some places (KOA's) wouldn't work with me and kept my deposit. There are National Parks where you absolutely have to have reservations, but most places you can find a place to park and drive in.
BTW, if your only reason to see Seattle is the Space Needle, they have a taller one in San Antonio that you see and skip this whole NW corner. I mean there is tons to see and do in the PNW but save it for another year and another trip.