We always camp where there are bears, sometimes in our TT and sometimes in our tent. More in our tent. We have had many a bear through our camp.
What you are using to camp in is not the issue when it comes to bears. A MH or TT will give you the feeling of being safer but it comes down to doing your homework and respecting where you are. There are many things people do that attract bears.
If a bear wants in he will get in. A solid side will not stop him. I have seen tens of thousands of dollars done to a TT from a bear.
Like I said...do your homework on hosekeeping and items in your sleeping area.