Since I had the tailgate out from the truck and was doing work on it anyway, decided now was a good time to look at performing the "tailgate storage" mod.
To do this, I admittedly just looked at what others have done in the past. I am not done yet, but in-process (with 50 other things).
First, mark out with a pen where you want to cut the metal. If you look at Trail Tailor, Wagon Gear or some others - you see that they use a lip and the holes that were in place for the old tailgate carpet as anchor points. Its important to not cut through your door latch, so use special care on this section (see the XXXs).
Next, drill a pilot hole.
Following this, bust out your jigsaw and a few metal bits ( I went through two). And do your best to cut a straight line.
At the ribs ( there are three ribs holding the metal in place) you can either use longer blades or bend the metal up and cut with an angle grinder.
Lastly, in order to get access to the ribs, you might need to knock through the spot welds with a chisel and hammer.
I've started to look at either fabricating a down and dirty wooden lid - with wood I have in my reserve pile, while also looking at buying a sheet or two of 6061 Aluminum. Either way, I will be using my beefy Festool router to round the edges and route out a lip for the doors to sit on.
Piano Hinges and compression latches are next up on the purchase list. I figure all in this will be a $250 project since its just raw materials I am buying.
This is my "budget" tailgate storage build.