[RC-Monster Mike]

Unless the battery is stuffed into the tray(big battery), the wires should not pose a problem with most packs. I am not sure how your little 4100mah 4s pack that is "swimming" in the tray has a wire interference? as far as an insert for placing smaller packs - I use a thin padded foam in the bottom of my trays - provides great traction and the packs don't move during use(could place a smaller pack near the rear of the tray and it will still be there at the end of the run).

I did consider the wire trail on the under side of the tray - the problem is that it would route the wires into harms way due to the big cutout in the chassis for the flywheel. It would be easy enough to make the trail available, but I wouldn't use it myself, as the rx wire leads would end up getting damaged eventually from track debris. There should be enough room to route the wire under the tray out along the mudguard and back to the radio box with the vecro strap - this way is safer imo. :)