I think this is probably our best option. Select the Storage/Parking link on the left hand side of the screen. I don't know if they have a daily rate, but I will look into it.
http://columbiacrossings.com/
Columbia Crossings can ease the stress of too many vehicles and trailers in your garage and driveway. We offer 35 covered and 170 uncovered spaces for trailers, RV’s, and vehicles up to 35 feet. The rates are reasonable and both facilities are secured with electronic gates and patrolled 24 hours. Access is 7 days a week from 7 a.m. to 10 p.m.
Columbia Crossings' parking facilities are just 1/2 mile from I-5, between Vancouver and Portland.
* Large, covered asphalt pads
* Ample turning radius for large vehicles
* Solid steel roof, minimum 12'6" clearance
* Public storage available onsite
Just minutes from the open road.