PolyCarbonate sheets at HomeDepot can be cut and make great covers... 5mm is good, 10mm is "bullet proof"
All my DIY Boxes, are made with 3/4" Purebond Plywood & topped off with a hinged polycarb lid.
1 Wee OOPSIE can make for a REALLY BAD DAY !
1st Rule of Crisis Management = PREVENTION !
1 of the 100AH packs.