I have done this now for two toolboxes as well as my welding cart
My first time doing this was a harbor freight 56" box. I riveted it to the top along the perimeter and made a front lip out of alum angle to keep stuff from rolling forward. The back of the stainless has a half inch tall 90* break
That was 2 years ago. The box was replaced with a snap on krl that I scored for 1200 bucks

Now let's move on to my snap on double bank. Snap on wants 7-800 dollars for their stainless top. Screw that I'll make another one. This time I went a little further with it. I made another front lip for it again that I notched out around the lock to give it a factory look. I riveted it around the perimeter but I went a step further and applied a 2 part panel bond adhesive around the edge to keep liquids from getting underneath and possibly rusting the top of the box. The back has a bent lip aswell. I built this for about $50

Masking off to apply the panel bond border

Any more pics of this you would like or info I'll help you out with.
Also did a little harbor freight welding cart that I added a handle to. It's got a bend in the front and a lip in the back
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