Trunk Mounted Battery in ERA SC

[Cobra 29]

Bob, the PO or builder placed the battery in the middle of the trunk (side to side) and against the rear wall that slopes upward over the rear axle assembly. Presently an inexpensive plastic box is used to hold the battery. The box is "secured" to the trunk floor by two l-shaped barackets and a nylon strap. The problem is that the L-shaped brackets and the plastic loops that hold the strap are secured with small screws into the fiberglass trunk floor. I do not believe this is very secure.

I have done several searches and read many responses including a few in the ERA forum. My question is what is the best way to secure a battery tray or box to the trunk floor or upper "shelf" over the rear axle? On the SC, both areas seem to be covered in a thinner fiberglass panel. Should I atttempt to bolt thru the selected panel and secure with a thin metal plate? If I select the trunk floor I believe I would need to remove the gas tank for access. The upper shelf is not completely level (front ro rear). Any suggestions from Bob or others and especially pictures would be greatly appreciated. Thanks