Thats been my only complaint about a123's - they're big. I did my 1st set into sbs as a 5S1P config and its big, roughly 140mm x 72mm x 30mm (l x w x h). This was super easy to do coming out of a Dewalt pac, one was already basically already made, other had to have extra connection between cells. Its the width of the sbs config thats the prob. I can fit it nicely behind the trans and motor on my flm Emaxx, but thats about it, can stack two back there for a 5S2P.

My next a123s will be 6S pacs in a stacked tube config - start with a dbl shotgun and lay another on top for 6S. I know it will fit the older E's trays, not too sure on the new one. Its for my G2R and I've seen them fitted so I know they work for that. The stacked tube is a lot more likely to fit versus a sbs config - I know that won't fit.