Most of the fitments have dimensions.
These are very similar to the "top on the line...CBT" units offered some time ago.
I plan on ordering one and drilling as needed.for fitment.
That or you can cut and make your own outta aluminum stock.
This is very easily done. Aluminum cuts easily with a jigsaw and sands as easy as wood. Hit it with a can of bed liner paint and you're away to the races.