Made this setup last season using a garmin striker 4. Mounted and sealed the screws with silicone. Attached quick connects for the battery, insulated with cut foam and triple layer on the bottom. Small rubber gasket fit for the power cable to go through.
It all fits inside and is packable. If you go with a cheaper SLA battery and look for a used striker 4, this setup can be made under $200 all in pretty easily.
Posted by sipthestew