Go looking for some pieces of perforated metal sheets, holes of .0938" or smaller (gauge with drill bit). make your square for the outside first, cut corners enough to make 90 degree bends. Put another piece on top and bottom and match up holes to screw together. Take apart and cut put back together and screw together with small stainless steel nuts, bolts, washers and lock washers. Top needs a plastic bulkhead fitting to fit pump hose. Perforated metal very cheap if you can find in scrap yard, 2" bulk head fitting  threaded should be under $8 dollars on eBay.