I have been using chastity devices for 6 years on and off, and I find that with most ball trap devices that night time pain from erections or damaged balls is what I get ? but the solutions I have found are..
1) make sure the cage is not too big.. go small to limit growth
2) lubricate your balls and the shaft regularly. I use baby oil with aloe Vera that seems to keep my skin in good condition
3) A boot lace as in the first picture. Pass through device one end around waist and back through device. Pull tight so that it pulls device in and tight to body and do a knot, not one you cannot undo. And as if by magic no night time pain from those attempted erections ?

Good luck
Lucy x