I have that mount and used it for both a 5lb and 2.5lb extinguisher:
View attachment 2635144
View attachment 2635145
It was fine if I was the only one driving the truck because I run with the seat all the way back (6' 4").
The problem came about when someone shorter wanted to run the seat forward. It was OK for a couple of inches, but as soon as the plastic "skirt" on the front of the seat hit the extinguisher, it was no go.
Even with the extinguisher removed, the seat skirt would hit the extinguisher mounting hardware:
View attachment 2635149
I even tried it with the mounting clips for an ELEMENT 50 extinguisher, but ran into the same problem.
My latest project is to try to mount one or two ELEMENT 50 extinguishers directly to the front of the seat on the plastic skirt. In theory, looks promising, but I'm still playing around with exactly how to mount the ELEMENT 50 clips - latest is 3M VHB bonding tape using a 2" x 3" metal plate between the mounting clips and the seat.
HTH