Yeah sadly to save vehicle contents you gotta put em into a box, theres stuff in the mission which empties then randomizes vehicle loot, and it isn't smart enough to tell whats a players vehicle and whats a map spawned vehicle.

Been saved orange area 1 killed enemy in car, I put my items in car when exit games then loaded games but some my items was gone just random items & free gun in car WTF. this mod can't save normal one still grey out. Beware! can't put own items in vehicle will gone when load games.