There are a few options for recoil units from okmo clark and dklm. Mine is clark. You need space below the turret ring for the breech and recoil servo to depress into without catching wires. My suggestion is not to have anything above the level of what was the stock battery box. This is a flat tank and hard to fit alot of stuff into , at least with a bigger battery. I also scrwed my hull together and am more or less going to leave the battery in even though i can get it out with effort.