I just completed my upgrade from the standard 12 volt battery to 2- 6 volt golf cart batteries on my Sundance 245RL 5th wheel. Surprisingly the larger 6 volt battery fit into the original battery case in the front storage compartment. However the battery was too tall for the top half cover. I made a 1"x 2" wood frame and attached it to the bottom half of the battery box. I then attached the top cover to the frame and it fits perfect. I bought a standard 6 volt battery box and installed it next to the existing box. I cut a hole in the top and installed a flexible vent and tied it into the existing vent by using a 1-1/2 inch ABS "Y" connector and threaded coupler. The flexible tubing fits perfectly into this sized piping. Attached are photos highlighting the project. Sorry, I couldn't get the photos to rotate.