Why a trailer costs less per night and closes more campgrounds
Travel trailers are the cheapest Seattle rentals at a median $126 per day and the most listed at 193 of 473. They are also the worst fit: Mount Rainier's White River campground caps trailers at 18 feet against 27 feet for motorhomes, so 20% of trailers clear it against 63% of Class C motorhomes.
How this was worked out
Mount Rainier publishes separate RV and trailer caps at every campground, tightest at White River with 27 ft and 18 ft. Seattle's 473 listings include 193 trailers at a median $126 per day.
Measured each class against the cap that actually governs it, RV limit for motorhomes and trailer limit for towables, rather than against a single length. That reversal is what makes the cheapest class the least usable.
What to do
Decide towable or motorised by the campgrounds you intend to use, not by the nightly rate. Check the trailer cap, which is always the tighter number.
80% of trailers are shut out of White River, after choosing on a rate $147 a day below a Class B.