I'm a big fan of pulling the subframes out to do major work or just a tidy up - but the body usually ends up right in the way because it is so hard to move. This simple frame took less than a day to make out of scrap 76 x 38 patio tube and some cheap castor wheels, but made life a lot easier.
It sits under the body where the floor meets the side panniers, and extends from the front subframe mounts back to the rear subframe. Back wheels can be left on, and are about 2 inches off the floor. I haven't tried it with the engine in, but don't think it would be anywhere near strong enough.
You could use whatever material you like, but I would imagine the body weighs around 400kg without an engine so don't make it too light. These wheels are rated at 105kg each, tek screwed to the patio tube and are a bare minimum on a smooth concrete floor. Go bigger and bolt them on for off road conditions!
The pieces on top are 4x2 treated pine, and the holes in the nearest one are for the bolts that hold the plate under the fuel tank on side fill bodies. You will need to crawl underneath to measure the bolts and drill appropriate holes for your Moke. The wood is supported on a strip of 50 x 3mm flat welded to the uprights and held on with a couple of tek screws. The uprights are 8 inches high.
The body seems quite stable once on and in no danger of falling off - but if you want to secure it there is room to put a tek screw down from the top into the wood through the 4 drain holes in the floor.
...and in use. Makes a good addition to the subframe cradle (but I should have painted it to match!).
Here are some basic plans.
Final total height depends a bit on the wheels and material used, but mine is 15" off the floor, and I have about 2"clearance under the back tyres. The bits of wood are at 29 1/2" centres - any more and the floor starts to angle up and they won't be supporting anything. Total length of the wood is a maximum of 53".