Re-use (as in real life) of the panzer IV chassis to make a selfpropelled artillery.
(Now that I had it made, I wanted to build one of my favorite pieces of german WW II equipment.)
Wow, this is an amazing build! I need to study it for a while to figure everything out. I admire the way you hinged the side walls to match the slope of the front. So much accurate detail in such a small model, this is how to do it! This looks just like a Hummel.