The ability to resupply a GV, either on or off-base, is accomplished easily enough with an M3 and vehicle supplies. In a typical GV fight where resupplying is necessary, there's also players dying and re-upping, and it takes only a couple of minutes of precious trigger-time to run an M3 around the base and drop supplies.
Strategically thinking players will drop supplies before an attack takes place.
In some instances, our squad has run M3s out into the trees with supplies and had them wait until they were needed. This comes in handy when the VH are taken down.
I've also noticed that in most instances, in the middle of a GV fight, someone will usually (and willingly) run supplies out to the GVs if the pressure is heavy, or if someone asks for support to land kills.
What I wouldn't mind seeing, is the ability to return to a GV base and move out to a spawn point without having to land and respawn. This would allow players with one kill and nothing happening, to move to another area to add to his total without driving 25 miles. Obviously, I don't think a player could be allowed to warp to a spawn point if the base is flashing.