No room for second battery

Believe me if it were possible, I would not be going down this road. The easy solution of a battery box or angle iron frame was my first hope and plan. Once I took possession of the unit and realized the limitations I looked for other options. Locating batteries inside the rig was not as desirable for the reason stated above. I remove my batteries after every trip to maintain them at my home instead of leaving them at the storage yard. I have tried to show the WDH mount for reference.The mount must be located here for proper installation. The chain should be hanging vertically when attached. This leaves no room for a frame. Admitting that I do have Redneck Engineering skills means if it were possible I would have gone down that road.