Cut some pieces of carbon-fiber large enough for the batteries, cut slots in them to run battery straps through, drill and countersink a couple holes to mount them to the chassis, and you are golden!
I did this very thing on my BL Revo 3.3 Conversion and it hold the batteries (two Zippy Flightmax 30C 4S 2650mAh LiPos in Parallel) perfectly!
-Chad › PM ME IF YOU HAVE THE BELOW: › VBS, CVDs, GM Single-Speed, OTB, Ultramaxxed, Super6, Strobe, Sprong, CNR Brake, UE Hex, DUH Towers, Predator, Blackbird, GA Blue Screws, HCR F/R Skids & Mutant