[techhelpbb]

I also ordered some 200x50 tires and the tube from Amazon without issue out of curiosity.

I also stopped by the local Tractor Supply and grabbed a 10" knobby tube tire from them: 4.10/3.50-4 which is a tubeless tire. I also grabbed the same size tube.

That 10" tire has just under a 4" opening in the center. 3" PVC couplings have just over a 4" external diameter. I wasn't able to press one into the tire stock even with some petroleum jelly to help. I was able to put the tube around the stock coupling. I put it on my MaxNC lathe, used a dial indicator to check the run out, and then turned it down ever so slightly on the external sides of my centering 3 jaw chuck (minding the internal taper of that coupling). Finished it with some light sanding. It can be made to fit now into the center of that tire and tube around it (minding the air fitting will need an opening). You can put a tube in a tubeless tire. Need a lip on it and something in the middle. Not sure frankly if this tubeless tire really needs that tube in it as it is pretty rigid on it's own and for such a light vehicle as this that might be enough.

Total weight of the tire and tube is: 2.4lbs
Total weight of the turned down coupling is: 0.43lbs
Wouldn't be surprised if the whole thing comes in at 4-5lbs per tire with a hub.

I don't much plan on building this out any further but I had a hard time finding a 10" spoked tire that someone could use for a donor rim. Will try the same trick with the 200x50 tire when it gets here. All the AndyMark tires I had are otherwise occupied.