Wut? 
How do you "exploit" score by using a field gun?
Making field guns count the same as a kill of a plane or vehicle is a dumb idea. Killing a Jeep is ten times as difficult.
What will happen is nobody will use the guns and there will be a hundred more de-ackers/vulchers fighting over the easiest kills imaginable.
well first learning what exploit means helps... secondly a jeep cant fire a 37mm round 3.5k yards out and take a plane down.. or 88mm flak rounds 15k yards out.. slight difference if the gunner is good it can kill the plane before it is close enough to kill the gun a jeep is limited to the same range.. as aircraft(With 50 cals) so both can shoot each other at the same.. time put a 20-37mm on jeep then we'll talk
but.. its quite simple.. people in base guns do not get a "death" their score does not get hurt but they kill the attacker.. never the less if its not AI Shooting at you it should be a kill.. that simple
also.. definition of exploit "make full use of and derive benefit from"
but people exploit it to avoid score loss.. more than last line of defense and.. its been problem.. for hmm 4-5 years now? same with ENY and bomb n bails..people leave for reasons.. and its not the economy when people wise up to this.. maybe we'll have a player base again