Battery trays made out of a stiff plastic box wasn't that sexy... but they got it up and running.
Time for battery tray v2. Found a stick of U shaped aluminium. Made a cut out in each end and bend them. tadaa... battery tray!
Added a strip of velcro to the bottom of the tray and the bat. will have 2 velcro straps around each tray. The straps are from lab top PSU's... they are used in order to manage the cable length.
Made a plastic insert in each tray. This way I can use standard hex screws. The "head" of the screws is sitting slightly lower than the edge of the plastic insert. Battery safe from harm... at least they wont get damaged by the screws ;)
Placed them at the front of the sav... should be ok balanced once motor + ESC is installed in the back.