RV camping at North Cascades
The North Cascades are reachable from Seattle without a ferry. Every island destination in this data set requires a crossing costing between $46.90 and $256.75 one way for a tall sub-30 ft vehicle.
Take the longest rental here, not to the islands. This is the only destination in the set with no ferry and no published length cap, so neither the 7'2" height band nor a campsite limit rules anything out. Confirm the site with the park anyway, because silent is not the same as unlimited.
Getting there
North Cascades is reached by road. No ferry means the 7 foot 2 inch height band never applies, which removes between $93.80 and $513.50 from a round trip compared with the island destinations.
Which rental suits it
No campground here publishes a length limit, so we cannot say which classes clear it. Check the campground directly before booking a rental around a site you have not confirmed. Compare published limits across every park.