This subject has come up here before, but usually as campgrounds not allowing old
trailers, more than small trailers. Some certainly do have strange rules (and some rules which make some sense after consideration, usually involving tents or tent trailers), but to allow some hardwall travel trailers and just not short ones would be pretty strange.
Certainly at Canadian federal parks, and I would guess federal, provincial, and state facilities all over the continent, sanity reigns and our eggs are welcome.
The couple of private campgrounds I have tried also welcome all sizes of trailer.
If anyone doesn't want my Boler
in their campground, I don't want to do business with them anyway!
Now if you want to see a really
annoyed prospective camper, how about the guy who buys the 45' Class C on a big truck chassis for more than my house is worth, then gets turned down at a place which only takes Class A motorhomes. What good is out-spending your neighbors if it isn't recognized?