I'd grab that Panther off you in a flash but it would cost more than the model to get here and well in more pieces that are in the box if you get my drift, nice collection..
My final build as far as last ground based ones go is a Trumpeter Kit 1/35 MORSER KARL-GERAT its a huge model with you being able to build an early or late version I opened up the box for a gecko at the parts sprues.
I umm! quickly put the lid back on, makes building a wind jammer a piece of cake it is a humongous model with a zillion bits!
The item itself in battle was so big, heavy and slow to move it was a tedious affair no doubt, the suspension system could lower and raise the carrier of the mortar there were 7 built 6 seeing actual combat service firing a 1.250 tonne shell 6.2 miles.
When lowered the carrier actually became the base for the system negating the need for any concrete pads or special ground prep's the only thing being of concern was slope and ground compaction, I for one would not want one of those rounds knocking on my door.