Zippy 4S in a 3906 chassis

I run a pair of FP 5s 3700s in serires and I have found that they have a similar footprint as the the stock E maxx holders they are just a tad bit longer which I cut out the rear of the holder and I don"t use straps but I use female velcro in the trays and use male velcro on the bottom of the battery...the batteries don't move and and the batteries don't heat up enough to cause problems with the velcro