I'm no modeller or painter so this is going to be a quick fudge. A quick of abuse by my household drill used in a highly unsafe manner to make a hole for the turret cupola and then a washer mounted on some green stuff to make the cupola. Note to those lacking green stuff: bit of blutac with a good coating of superglue also works...
I chopped off some excess gothic bits to reuse as a hatch or other bits. I thought about removing the spikes but still Hun enough I think. The removal of a gothic axe leave a very good steam claw.
The driver is a spare figure I had , some form of aeronaut. Helmet goggles, steel mail mask and body armour. I chopped off his legs and bent arms so at least one is on control lever extension (piece of wire). He is actually old school 25mm so bit short/skinny when on the ground but nobody going to argue with him in Otto as the 'Eisenmann' is known.
Bit of appropriate plastic pipe and another drilled hole to add a periscope for when the beast is 'closed down'. Finally I filled in the front 'head/helmet' space with more green stuff as that was bit to fantasy gothic in look.
I may drill out the gun barrel and I need to add a cupola hatch , but making a proper locking wheel.
Now to ponder the paint job, but will need a big Balkenkreuz and 'Otto' scrawled in chalk somewhere...