I have a 2004 3100SS and have been looking for a sliding battery tray. The trouble I'm having is that I really don't want to cut the side of my RV to accommodate the sliding tray. My existing battery compartment opening would need to be enlarged to handle the tray (and batteries).
I found a site that sells sliding battery trays (with specs) that may help you out, Fleming Sales - Trays
Let me know what you decide, I'd love to see what you do.