@Fred W. Hargis Jr You asked and this is it. I do not have a welding machine which would have been the best way to do this so here goes. I had some metal parts around the shop so I cut an aluminum plate for the floor. Bolted this to a Al square and bolted this to a 2x6 treated (I think). Bolted a small Al angle to the front of the plate. I had some metal corner plates from my grandson's swing set and those are the ends bottom is attached by some Al angle to the ends. All painted black.. .....

All kinda slammed together but now for a dilemma ......... how to hold the tool box in this tray . Debated bungee..... too weak and sun deteriorates those things. Tie down strap ..... too cumbersome to open and tie down. So hinges and metal comes to mind. Going to try a bit of metal I have . Will have a hinge at the top back and well you just have to wait til I finish.

So here is the finish.

Decided on strap to hold box in . Just quicker than going with metal.

Parts laid out for mounting. Had planned to use 2x but remembered that I had this aluminum pipe stock.

This is the box installed on pipe. Used rubber under connections to protect paint and hopefully stop rotation of the box. If needs ca add a screw.

Side view, note can slide a handled tool in pipe.

And the view from behind.

nice; I might have to borrow parts of your ideas, if you don't mind too much😁

Great idea Gerald, necessity is the mother of invention.