Good advice from 16ACE27 above. The under step compartment on the Axis/Vegas is 26 1/2" wide. Two Group 31 batteries which are 13" long will just fit.
It is almost impossible to find true thick plate deep cycle Group 31 batteries. I replaced my G27s with a pair of Windynation 100AH, Group 31 AGM batteries. AGMs work fine in deep cycle service.
See:
https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1
David