Here is an update on my battery box mod. Unfortunately I could not complete this mod. All the measurements I took would appear this mod was the ticket. The only way this mod would have worked was if I moved the propane tanks tight against the power tongue Jack. Doing this I found the propane hose from the regulator to the TT was short by 9 inches.
Yes I could get a new hose but I found other issues.
The lid on the box was also too tight against the front of the TT only allowing it to open only 1/2 way. Bottom line is I am lacking the real estate to do this on the A-Frame.
I ended up ordering the B&D RV Battery lock others have mentioned here. I'll find something later on that will fit
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2019 Jayco 26BHX Eagle HTX Fifth Wheel
2018 Chevrolet Silverado Double Cab 2500HD 4X4 6.0L 4.10 axle
Reese 16K Round Tube Slider Hitch
HD Trailering Package with Integrated Brake Controller