check Craigslist.
I spend $95 a month for a 30' long space with a roof over it in Vancouver, on Padden Parkway, just west of the Costco.
Many of the places that I found where in the same price range, and not covered, and most RV parking facilities where full when I was looking for a30' space. If you measure the truck and trailer, the overall length will be in the 44' range, that is much longer than I am, and will cost a bit more. you might want to store the tow vehicle at home, and keep moving it to avoid benig fined.
Good luck,
Fred.
