Do you have pictures of how you did this?
All you have to do is cut a rectangular hole in the bottom just big enough to install your cooler and fan.
Get a 4" or 6" wide x 1/4"thick piece of alum. flatbar, with the tanks rect. cutout facing upwards, slide your cooler into the opening,
positioning the flatbar to mark the hose openings that will be needed to route the hoses thru that flatbar. I drill the hose holes just big enough to slide the hoses thru the plate connecting the cooler withhose clamps.
Drill 2 holes thru the alum plate, on each side of the rect. cutout, and tap the spun alum tank for 3/8's NF threaded flathead cap screws. That will fasten the tank down to the alum. plate.
Now, that plate I drill about a dozen 1/2" thru holes of cooling. After I mount the alum. flatbar with the tank upon it, I fasten a small scoop onto the bottom to grab air when the car is moving. The scoop doesn't have to be big, because the fan will pull the air in thru the bottom, but at speed, it will be assisted by that scoop.The cooler is held in with a couple of larger pieces of hoses going over the hoses that feed the cooler. These are fastened down with crimp clamps, This allows the cooler to jiggle and move slightly over rough roads and bumps.
Drill 2 or 3 large holes in the ends of the tank. I fastened a alum plate over the holes, with the plate having 2" spacers holding the end plates off, but end plates dia. has to be bigger that the part with the holes, that way you won't see them, they'll be kinda hidden.
Now, going down the road, the small scoop on bottom will shove alot of air thru the tank, thru the cooler and out the cooling holes in the end of the tank.
Sorry, my camera is broken and my wacom pad is screwed, too. Someone dropped something heavy on it....