Securing Single Cab Sub Box

Looking for some suggestions on how to mount this subwoofer box in my 2003 Silverado Single Cab, running 2 Sundown E-10 v.3’s and I don’t want them hitting the back of the seat. I would prefer to not drill any holes if I don’t have to so I’ve come up with a bracket, pardon my terrible drawing skills. I’m thinking I can make brackets out of steel, 2 that go underneath the OEM seat bolt, and 2 that be either screwed directly into the box or re use a mounting screw on the sub. Was also thinking of possibly running a strap down to the seat rail and to the child seat spot behind the middle seat. Any ideas? Thanks in advance y’all