I went to a car audio place, and got a starting battery - agm like the rest of mine. It is about 3 inch by 8x8. I am thinking of using a battery tender like device to charge it off ac power. When I get over these darn allergies, I am going to get back to the project.
2007 Chevrolet 3500 CC/LB Duramax/Dually 4X4 Mine r4tech, Reese Signature Series 18k +slider, duratrac, Titan 62 gallon, diamond eye, Cheetah 64
2011 Keystone Fusion 405 TrailAir & Triglide, Centerpoint, gen-turi, 3 PVX-840T, XANTREX FREEDOM SW3012, G614