mine are from old license plates so they have holes. But without the holes would be able to fill them full of water and they wouldn't leak!
I've entered this project in the REUSE contest, Check out the entries and vote on one you like! :D
Step 1: Layout.
this will be a bit more self explanatory in the next step, but your corners should be marked like the photo. My container needs 1/4in of lip for folding over. .
Step 2: Cutting.
cut away ONLY the blackened area on the drawing. this will allow you to tuck the corners making the water tight seam.
Step 3: Pre-Bending.
using a screwdriver or wide, blunted chisel, slightly crease the corners. the 45 degree creases will be towards the top, and from the top. the 90 degree creases that follow your marks will be towards and from the bottom. when you're finished creasing lying flat your part should be held up by the corners only. if not, something's wrong.
Step 4: Folding. EXTREMELY IMAGE HEAVY!
folding is a process that should be taken slow, hopefully I've provided sufficient photos to walk you through it. start close to a corner and fold towards you if using a vise. help the crease fold outward with a screwdriver and pliers. when you move to the next side stay close to your best looking corner and pinch the corner crease while folding towards you. repeat on all sides. when each crease forms a triangular "ear" you're ready for the next side. put a block in your vise (wood works for soft metals) and fold the ears over making sure they lie straight. repeat all 4 sides. last step Is the edge fold, necessary to lock the ears down and strengthen the whole container. line your vise jaws up and bend CAREFULLY!!! at this point you might tear your corner seam. put your block back in the vise and hammer flat. YOU'RE DONE!!
Step 5: In Conclusion
My containers are made from old license plates and as such have holes in them, but as you can see, the corner is water tight. This technique can be used to make custom sized cookware, condensate pans for AC's and even water troughs for livestock.