According to NFPA 52 there is a requirement that the CNG cylinder mounting must have a backing plate (on the other side of the sheet metal) with a surface area of 7 sq. inches or more. So with that I set out to inspect the underside where the tie down mounts are located.

There are three tie downs at the front of the main mount bracket. The right and left look as above and need no modification. They have a large backing plate with an integrated threaded boss.

This is the center front backing plate. It is also built similar to the right and left backing plate. So nothing needs done here.
 

However the rear tie downs relies on a bolt welded to the edge of a support channel. So a backing plate needs to be fabricated. So I cut (2) 2" x 4" and (2) 2 1/4" x 1 1/2" out of 1/4" bar.

Here I am milling out a slot so the backing plate will clear the existing nut.

Here the milled plate is positioned for welding.

The 2 1/4" x 1 1/2" pad is positioned above the milled slot and away we weld.

Notice the heavy slag left after the weld. The 7024 welding rod has an extremely thick flux coating made up mostly or Iron, Manganese and Potassium Silicate with other trace elements added in.

However when you chip away the slag, you always get a great or decent looking weld.
 

Here the right and left backing plates are marked for drilling.

Here the plates are drilled. I had to grind a chamfer on the inside to clear the bend in the support channel that the plate mounts against
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Here the passenger side backing plate is installed. It is a nice clean looking solution to the original problem.

Here is the drivers side backing plat installed.

The front and rear tie downs only provided 5 mount points. An additional 8 mount points were added. The above pic shows two drop down mounts with 4 mount holes each and matching backing plates that install under the floor.