You could mount it vertical just in front of the center portion of the seat. It's visible and center passengers can put their legs over or around it.
Another option is on the roof. If you have the center overhead consul, you could build another with the CB tucked into the back of it (fabric insert just below the CB's internal speaker). Maybe add an external speaker just below the dash.
I did the overhead consol mount in my '94, worked great. Sorry no pictures, truck has been gone for 4 yrs.
Imagination is you only limitation.