Mounting Battery Box with Two 6V Batteries in Rear Compartment

[Axeman]

I’m installing 2 6V batteries in a battery box in the rear compartment of our 2720QD. I’ve researched fairly extensively on this site to see how others have done it and would like to use an approach similar to the pictures below from posts by Michael and Wavery respectively. I’m trying to determine the best way to secure the box in place. The first picture appears to use a 4x4 wrapped in non-slip material to hold the box in place, but I can’t tell how it’s secured to the TM (Michael’s no longer active on the site or I’d ask him). The picture on the right doesn’t look like the box is secured at all, but it may have been taken before the project was complete or I may just not be able to see how its secured.

If anyone has any insight into how substantially the box needs to be secured and the best way to do that, I would greatly appreciate your input.

Thanks,
Todd