Avery First, trying to avoid weak times by doing things like showering in the swimmer's wetdown area where one could not touch oneself without risking discipline. Not drinking which weakens one's resistance, not going to places like bars where boys will approach you, no sexy undies which turns one's thoughts to sex, etc.
You have thought carefully about when it is a risk and how you can minimise it. Very good.
Avery Second, keeping the belt handy at times when temptation presents itself, e.g. when showering alone is the only alternative, under the bed when the hands begin to wander at night.
A CB is a good tool for precisely such situations. Your solution is certainly a good way, but there is a risk that someone could take the key. In this case, a box with a time lock is a safe way to store the key and then remove it in the morning.
If you want to give it a try, opt for a box that you can open with force if necessary. For the worst case situation.
