My RV is a fixture at several road courses. I love Petit Lemans, but I did not make it this year. I think I should be back next year.
Anyway, it is not in the Northwest, but anyone into racing that can get to Florida should go tot he 12 Hours of Sebring. Best sports car race in North America.
If you are in Wisconsin check out Road America. Fantastic track. They host NASCAR Nationwide and sports car events.
Virginia International Raceway is like a country club. It also has good trackside camping.
Barber Motorsports park just outside of Birmingham, AL is a spectacular track. You can camp on sight, but they do not have any trackside spots. They have an Indy race, and several motorcycle events a year. Still worth the visit. Even if you are just driving by STOP there. They have an incredible motorcycle museum that is a must see.
Now on to the Northwest. I have never traveled up there, and am not familiar with any big races up that way, but Portland has a track that will host some racing.
The in Northern Cali, Sonoma, is a road course that hosts for NASCR and Indy car events.
South to middle of California you have Leguna Seca in Monteray, one of the tracks I really wnat to visit one day, that hosts the same series as Petit (well kind of with the two big road racing series "merging" it is all now under the USCR banner and not ALMS or Grand Am).
If anything else pops in my head for the Northwest I will post, but sadly that area of Washington state and Oregon seem to be left off major race series schedules.