measure fuel in gals , liters, pounds, etc, instead of % 
field fuel bunkers will each have XXXXX gals of fuel , when you put XXX gals in your plane, the fuel at the field reduced by that much. field fuel bunkers are resupplyed by convoy and/or C47, ammo could be treated same way. 
if a fuel bunker is destroyed , fuel is lost. 
this makes more sense than %, this also gives a field a finite amout of fuel over a set time period (unless resupplyed by players, C47, M3 ), this may slow down the endless reupping from fields. 
44MAG