Did you lengthen the chassis? The Hull and tracks on the Nashorn and Hummel were longer than a regular Panzer IV. I can't tell from the 3D design, but the gun compartment looks a little short.
Excited to see War Park do a Nashorn. Please do a Hummel too as all you need is a different gun.
The perspective of 3D model is different from that of real object. The size is strictly referred to the size of the real car.