I would not camp in bear country in any type of soft-sided camper or tent.
Yes, it can be done safely. But it is a HUGE pain in the behind. Any food, drinks, cosmetics, and toiletries that you are not using at any moment, cannot be left in the camper or tent. They must be in a bear box provided, or LOCKED in a hardsided vehicle. Very very unhandy. I've done it, and won't do it again willingly.
So far as the length---smaller is better. Even the smallest campsites will accommodate a 22' trailer, although some might be tight, and you won't be able to park in front of it. And some are huge. It varies widely even within the same campground sometimes.