[BrianG]

The 2s packs I used were 2s2p, so 4 stacked cells per side. 3s1p per side should be thinner.

But, to get the clearance for the shell with 4 stacked cells, I had to raise the body mounting a bit. If you don't mind a sloppy looking setup, you could just velcro the packs to the mudguards (I use actual trays) to gain a few mm's.