Pegasus Hobbies have some spaceship kits including a UFO that is just the right size. My brother and I amused ourselves at it's expense at one point by setting some spare Solido/Verem diecast tank turrets on it, as in some of those daft Nazi UFO pictures. I am slightly embarrassed to say that it looked quite good with them.
The intention was to build it straight from the box but to put some hard edged camouflage on it in greys. Hinting at a Luftwaffe colour scheme but more as a in-joke than anything else.
The pictures of the Chinese APC conversion remind me of an ancient Rhino conversion I did years ago, It was with the old style Rhino. The nose was built as normal and a box hull extended behind it. The two halves of an ancient Airfix space shuttle SRB nose cone were added to each side and thrusters from left over lorry kit wheel hubs and some additional detail parts, including bizarrely moving flaps, added. It looked quite good but as that old Rhino was chronically undersized it was a better match for 20mm figures than 28mm ones but it is maybe an idea worth revisiting.
I really like the Star Wars republic gunship and a slightly larger model of one would be perfect though the roughly 20mm Revell one has been used very successfully with 28mm figures. I wonder if I could graft the cockpit from an OV-10 Bronco onto one?