Hi Tempest.
Any hard case single cell lipo will fit into your mardave. You may also find that they fit into your standard battery mounts. However if you are struggling to get your car up to the weight limit (normally 1kg for brushless and lipo) then the standard battery trays waste a lot of space that weight could be placed in.
All I did is make two small carbon brackets to locate the lipo. Then tape the battery in:
Hope this helps
Karl