They make locking file boxes that are fire and waterproof. Check walmart I got mine for 50 or less to keep the deed to my home, car titles, tax returns, etc in. It's probably perfect for u bro.
Should be smarter than that & be responsible enough to keep your stuff away frm your little bro. Weed isn't suppsed to be a drug that runs households. For lots of us it's our meds & we take our precautions with our meds. Don't need "mommy" to make me stash my shit.