I have a E450 cab, not an Axis, but I have a Garmin 760. I installed mine using a RAM mount. I bolted the attachment ball to the storage bay in the "doghouse".
I actually bought a new doghouse on eBay as a spare so if I ever discontinued using the 760, I could replace it and have no screw holes showing.
The problem with the 760, or any of the 7" screens is they are big and heavy, and normal attachment methods may not work very well.
The only thing that works on a RV is the owner...