I made two slots going perpendicular to the length of the trays, for velcro straps to fit through. The velcro straps I'm using are similar to what Tekno sells, but I made them to save myself money

. Granted my Savage is using 2 Tekno trays, each with a Rhino 4s 3700mah pack (8s is what the ESC sees...).
SH Z-Car, Custom Crawler, 8s Savage,
12s XTM XLB 1/7 buggy,
4wd 4-link rear/IFS Pro4 truck,
Custom Hyper 10 Short Course,
Belt-Drive Mammoth ST 1/8 truggy, 4s 17.5 MM Pro HPI Blitz