If it were "my" truck (not owned by me but the one i use daily) here is what i would do.
I would get something like this:
and mount it to a piece of 1/4" steel plate, about 6" x 6" using countersink head bolts so that the back of the plate was flat.
then i would get something like this:
and add some sort of handle to it.
found here: https://www.zoro.com/mag-mate-cup-magnet-95-lb-pull-mx3000/i/G5400087/
Looking at the pic you posted, i would choose that little area toward the very top of that fiberglass cap that is on top of the cab, and stick the antenna mount on the outside, and the magnet on the inside.
now you would have a make-shift magnet mount antenna on the side of the cab way up high.
then i would get an antenna such as this (or similar of course):
found here: http://www.gijoesradioelectronics.com/scripts/prodView.asp?idproduct=1171
there would most likely be a few SWR issues to take care of but that could be taken care of with some counterpoise on the mount.
I am not a truck driver, so take this idea with a grain of salt, but maybe it at least creates some actual good ideas in others minds.
LC
