Completely forgot to update this thread! The Knight is in the process of being painted.
Some WIP pictures:
I've magnetized the waist with a couple of magnets in the legs and a screw on the cockpit:



Made a small interior for the cockpit, with a pilot (GW Tau pilot body and GW Imperial Guard Tank Commander head) and a seat/control panel from a small 1/35 helicopter:


With the upper armor attached:

Front view:

From above, with more details glued:

For the base, I've used plaster, mixed with sand:

After it dried, I scored the hell out of it with some metal brushes, until the sand gave a nice texture to the plaster:

Then I proceeded to glue some drinking straws (aka pipes) on the original plastic base, with some pieces of spare plaster:

Glued everything together with a special mixtures of white glue; wall spackling paste and a little water

After that I decided where I wanted the Knight to stand:

Marked it:

It took some days to harden, but it's now rock solid

Then I drilled some holes on the middle of the feet markings and put a long bolt and nut in each, secured with green stuff and superglue:

Same green stuff/superglue was used to secure some magnets on the feet:

This is how it stands right now:



The magnets have enough force for it to stand a casual bump on the gaming table.
Since I'm going to use it in my future Weird War 2 German force, I'm still planning on the final painting scheme. Right now its still just primed in black.