Seven Feathers Casino, not too south of Roseburg Oregon, has two nice options for RVs near their casino. First is the "RV Resort" which has an indoor pool, very nice pull-through sports, etc. and will run you around $100/night.

Or, you can follow signs to the "dry" RV camping just on the east side of the casino. As far as free casino spots go, this is a pretty nice one. No construction, not too bad for highway noise all things considered. There's even a large green grassy area if you want to get out and stretch your legs.

It's for self-contained RVs only, so make sure you have water, bathrooms etc., though you can also eat dinner or what-have-you at the casino. Maximum of five days stay. Generators are prohibited 10pm-7am, which helps keep the noise down.