I'd rather do two tandem bays running the long way than try to squeeze into 20' spaces. Passenger cars and small SUVs start at 16' and go up from there. A Tahoe is 17.5'.
20' exterior dimensions is going to net you right around 19' usable interior.
I use a "super" heavy duty Pucel cabinet for ammo storage. 12gauge steel. Weighs about 750lbs empty. No need to bolt it down when it's loaded up.
They've also made custom cabinets for me.
A company like Pucel can probably customize a locker design for you to exact size.
I don't think with your space constraints, anything that fits in there is going to be much more than a metal storage box.
That Schluter SS trim is serious stuff. BTDT.
I used the angle grinder with this wheel:
https://www.homedepot.com/p/DIABLO-4-5-in-Diamond-Wheel-for-Metal-Cutting-DDD045DIA101F/301454106
Cut slow with the material clamped to a sacrificial board.
May or may not be the right tool, but that's how...
We were certainly watching when a half billion of our dollars disappeared in the trash heap that was Solyndra.
Where were all those wonderful government watchdogs on that one? No need to reply... we all know the answer.
Huh?
My car was still under manufacturer's warranty. That's a quite a bit different than a half century old piece of machinery from a company no longer in business.