Maybe trucks coluld be an off board abtraction of the overall motorization of your army. Right next to your tech chips you would put the trucks you have purchased. Each truck costs 12 IPCs and allows you to make addtional attacks after your first combat phase. Each truck allows you to attack again with 3 infantry/artllery or 5 tanks/fighters/bombers even if these units have already battled. For the second attack tanks have a movement of 1 and aircraft of 3.You do not lose the trucks each time you use them and you can buy more of them each turn. You do lose one truck for battles in the second attack phase for every 5 units the enemy kills, but only if you lose the battle.
I think 12 IPC’s is pretty costly, but that is becasue it is a special investment and is not neccisarily purchased every game by every country.