If I am camping with the bike in sight of me I just lay it gently on its side or lean it against a tree. When I'm going to be backpacking or canoeing away I hide it in the woods, out of sight of the road, even sometimes with brush piled on top. If you're in a busier place with lots of people around a lock would be handy. I would not want it in the tent, I would think that would be a good way to get chain oil on your sleeping bag and everything else in there, unless you have a really huge tent that would be heavy to lug around on the bike.
Zach