Heavy-duty storage boxes are designed to take a lot of abuse. They need to be stackable, weatherproof and easy to move with the right equipment. Marine-grade plywood with multiple coats of clear acrylic wood sealant resists moisture damage. Stock-timber construction reduces wasted materials. Corner brackets provide extra support during movement inside or outside the warehouse, basement or garage.
Cut marine-grade plywood on your table saw to 1.2 m by 1.2 m (48 inches by 48 inches) sheets. Smooth with a coarse and medium belt on your chosen sander.
Cut eight pieces of stock timber to 116.25 cm (46.5 inch) lengths and four pieces to 106.25 cm (42.5 inch) lengths. Mitre the ends of the 116.25 cm (46.5 inch) pieces to a 45-degree angle. Smooth with a coarse and medium belt on your chosen sander. These will make the top and bottom frames for the storage box. The 106.25 cm (42.5 inch) straight pieces are the uprights of the box frame.
Sand and seal all box pieces with three to five coats of clear acrylic wood sealant.
Assemble the top and bottom frames by butting four pieces of mitred lumber together to form a square. Secure the frames using 90-degree corner brackets and 6 mm (1/4 inch) diameter, 3.7 cm (1.5 inch) long wood screws.
Have a helper hold the 5 by 10 by 106.25 cm (2 by 4 by 42.5 inch) frame supports on end while you position the bottom frame on top of them. Use a carpenters' square to ensure the pieces are flush with the wooden part of the frame, not with the corner brackets.
Remove one corner brace. Drill through the holes and into the uprights where needed using a 3 mm (1/8 inch) diameter bit. Replace the screws that go into the uprights with 8.7 cm (3.5 inch) ones and secure the corner bracket back in its correct position. Repeat until all four corners have been drilled and replaced.
Turn the frame over with the bracket side against the floor. Repeat removing the corner braces one at a time, drilling the necessary holes and replacing the shorter screws with the longer ones until the frame has been assembled. You will now have a cube with no sides.
Position the frame on the first sheet of 1.2 by 1.2 m (48 by 48 inch) plywood so that it is 1.8 cm (3/4 inch) from the edge on all four sides. Use a carpenters' pencil to mark the correct position for the frame.
While a helper keeps the frame steady, place one sheet of plywood against the frame, flush with the edges of the sheet on the bottom. Drill holes through one corner at a time, through the plywood and into the box frame. Secure the first plywood sheet using 6 mm (1/4 inch) diameter, 8.7 cm (3.5 inch) long wood screws spaced every 5 cm (2 inches), beginning at the top right corner. Repeat until all but the top plywood sheet has been attached to the box frame.
Place the item or items to be stored in the box. Attach the remaining plywood sheet using 8.7 cm (3.5 inch) wood screws.
Make test cuts on scrap wood before making the mitre cuts in your frame pieces. Use a combination square to check the inside and outside edges of the frame to ensure 90-degree angles in each corner.