The chassis batteries are specified by the chassis & engine manufacturer .
My 99 chassis with Cat engine calls for two 950 CCA batteries .But your 2008 could be different. I got my set at Auto Zone eight years ago and they still test fine.
If the batteries in your coach aren't original , and your worried they could be too small; a call to the chassis manufacturer with your serial number is in order.
99DSDP 3884, Freightliner, XC, CAT 3126B, 300 HP /ALLISON 3060
2000 Caravan toad, Remco & Blue Ox.