Are there air holes? Can you open it from the inside? Is there any way for someone to lock it from the outside so that you would not be able to get out without assistance?

If the answers to those questions (in the order given) are 'yes,' 'yes' and 'no' then it is probably okay for you to hide in it, but I think maybe you should try to come up with a better idea.

If you and your pesky brother don't share a room, ask your parents if you can put a lock on your door so that they can access your room, but he cannot.

That way, you can get some privacy without putting yourself in any possible danger.

If you and he share a room, then try to talk to your parents about your need for some brother-free time. If they cannot help you to get it at home, then ask if you can spend some time away from home doing things without your brother.

If you can schedule several activities which you can do during the week (without him along), you may find that you are able to tolerate him a little more when he does follow and find you.

Good luck, hon.