I prefer a minimum of 3 as it is the magical number of penals needed to one shot full health OKW buildings.
I am destroying OKW buildings in the first 13 minutes. Walking up to Schwerer and dropping the hurt while losing 4 models across 3 squads. Then doing it again a few minutes later.
How to bake one OKW truck.
1. get 1 mortar, 1 engie and 1 penal.
2. put all 3 units in range.
3. drop smoke on truck.
4. move in engie and penal, and start planting a demo.
5. 2 seconds before the demo is layed, throw one satchel on top of the demo.
6. enjoy your cooked german truck!