first of this thing will never have good aero... it's designed to be perfect off road, and just that, so on road it will always be handicapped. So not driving it sensible and slow is your best bet...
but here's an idea that might be inspiring... it's not too extreme,cheaply doable and testable, and for the most part won't compromise the vehicles off road performance... plus i don't think it would be to noticable to other drivers if propperly done..
it's mostly for inspiration, so i went all the way, but taking parts from it that are more subtle should also help
stock, modded, and highlighted.
main thing is an angled plate in front of the grill... this will deflect air over the grill, but basically not block it, as the sides are open, so it shoudld retain full off road cooling.
than you see that the front tires are virtually fully exposed.. what this vehicle could use is a huge airdam, so perhaps fabric or rubber "inverse mudflaps' that connect the mudguards to the bumper could be a start, than closing the bullbar (or whatever you have) and extending it as far down as possible...
if you really whant to go low you could make the lower part hinged so you could fold it up offroad.
or retain a sensible height and make the lowest part from strong rubber so that when it does hit something it will fold back....
a vehicle this aero dirty i think has the best fighting chance when the air is deflected as clean as possible around it... once that's done there's not much clean surface to keep the flow attached to and the vehicle's to short for much boattailing.