The Germans focused a lot of effort on mechanization of artillery. They were the first to use SPGs of all types in large numbers. The most common German fully tracked armoured vehicle was an SPG. Light and medium SPGs were common, but heavy ones not so much. Only the Jagdpanther heavy tank destroyer was built in large numbers, but only 90 Ferdinands and 85 Jagdtigers. Compared to the ISU-152 and ISU-122 these are negligible numbers. Heavy "weapons carriers" were in the worst position. Not a single one was mass produced and only one prototype was built. This was the Geschützwagen Tiger für 17cm K72 (Sf) or Grille 17/21.
A bigger weapons carrier