How about some mines. Use Ju88's to lay 3 sea Mine per plane, and Jeeps to lay upto 3 land mines. Mines could stay active for 15 to 30 min then they melt away like Gv sups do. Would have to do something with Land mines not being activated on own base though to stop gaming the game at map rooms.
We could also use the Boston for air mines but prolly to hard to implement. Akin to running into a chute I suppose.