While I realize that if you have ED you need something big to take it's place. Mine, however, still works.
A removeable frame made of small diameter exhaust pipe with two SKSs mounted side-by-side atop the frame work just fine.
Regulate the sights so they are synched at 200 or 250 yards. Watching for the bullet strikes will then tell you the range.
Mags for this should be Beta mags with atleast 1 reload per rifle, but as many as you can afford.
My choice for a mounted dual M-2 would be nothing less thyan a Dodge PowerWagon, and again, the sky's the limit.
I would however have a .50BMG single shot or repeating bolt action in the Jeep for that 'special' anti-materiel situation.