I have a
TorkLift battery box on my trailer and it uses a nylon woven strap to run lengthwise under each of the two batteries and then buckles on top. The strap runs in a grove in the bottom and under a couple of cross pieces at the ends to keep it in place.
i also put a
Battery mat
lining the entire box to absorb any possible acid spills that may occur during charging. The underside of my lid I put a heavy rubber lining glued to the top.
This setup has worked great for the past 5 or 6 years that I've had it.
Barney
