The Kubelwagen is a very fragile unit, gunfire will easily force it off. It needs to sit still for 1 and a half second before the suppression comes in effect, and any movement will disrupt it. The easiest way to take care of it would be to attack from another angle with another squad while it attacks the first. It'll take damage quickly even from Rear Echelon Troops or Combat Engineers, and will probably fall back.
If there are Sturmpioneers repairing it, target them instead. A classic case of "shoot the medic first", units take 200% damage while repairing or building. He'll either need to stop repairing and possible pull back, or you'll inflict expensive losses on him. Sturmpioneers are very expensive to reinforce, so it's not likely he'll sacrifice them to fix a little car. With them gone, the car will be easier to get rid of.
