Writing Letters at Basic Training

My boyfriend leaves for Fort Leo next week for his basic training and I’m going to miss him dearly. I know I will be able to write letters to him and I plan on doing that but he has a bad memory and I’m afraid he will not memorize my address and as a result, I will be unable to get his address in order to write him. Do you all think I could write it down for him and leave it in his wallet or something or no? I know that their belongings get locked up so I didn’t know if that would be a good idea or not. Thank you all in advance!