Unfortunately there aren't many RV parks in the Vancouver area. Burnaby Caribou and Capilano are the closest to Vancouver. The Fort Langley Campground is nice but 40min outside of town. EagleWind RV park in Aldergrove is probably the newest and cleanest park in town but 45min away. Pacific Border RV park is another option (45min from town and about 35min from the ferry). None of the parks will be cheap.
Doing a day trip to Vancouver Island is possible but difficult. You may need ferry reservations to make sure you get the sailing you want. You'll spend as much time driving and waiting in ferry lineups as you will on the island.
I was born and raised in the Vancouver area so if you have more questions let me know. I'd be happy to help.