Decided to design a new Odyssey PC625 battery box since the one included in the OneX plans would have to be modified anyway, if you ever want to remove your battery ;).
Decided to use a 2 1/2 angle for the base support with 1 1/2" hinges .040 thickness on each side and a 1" angle along the top. I'll use .032" sheet aluminum to wrap around the battery and hold it in place. I will also use 1" wide by 1/8" thick backer plates on the backside of the FW. This design will allow battery removal by simply pulling the two hinge pins which will be safety wired to the top angle.
The Sonex plans do not show any bracing or reinforcement for the battery, I assume they just attach it to the stainless steel FW which is probably OK but I think I will run a 1" angle horizontally and tie that into the side and center FW braces. Probably unnecessary but I will feel better with it braced since it weighs 13 lbs.
I attached a couple CAD drawing of the box and will follow-up with pictures of the actual installation.The attached 3D drawings are not current but close enough to show the basic design idea.
