Back in the mid 80s, shortly after we camped at Lake Louise in Canada ... a grizzley came into a tent and attacked two campers.
I read that Lake Louise campground is having so many bear problems, that they installed an electric fence around the tenting area of the campground this year... For the past two years (2001,2002), they did not allow tent or pop-up campers into the campground ... only hard sided trailers or motorhomes.
For whatever reason, bears quickly associate tents and pop-up trailers with easy pickings ... yet for the most part, leave hard-sided trailer alone.
However, a couple of years ago, near Fairplay, Co, at a commerical campground, where people rent campsites and store their trailers there year-round ... during the off season, a hungry black bear tore off the door of every trailer in the campground and rummaged around in search of food ... because the bear had once found food in an hardsided trailer.
The bear was caught and killed because forest service folks thought it could never be "untrained" and could possible teach other bears how to break into trailers.
All in all ... I'm more afraid of a human than I am a bear.