Very cool ... found a better design, easier to build, and not very expensive either. He'll have to stay in the rooms there is enough space to turn around in but that has got to be better than being limited to wall hugging. It is basically a square frame, casters on front and back legs, with material stretched across the interior to support his whole body. If I put a zipper or buttons on one edge of the material, I can set the cart down over him then pull the saddle underneath him and attach it to the other side of the frame. It would be far easier on him (and me) to get him up on all fours than to lift him up completely and try to set him down in a harness.
Here is the basic concept:
Yes, I know for some people this seems like alot of trouble for one old dog. But, this old dog has been mine since the minute he was born - his parents were my dogs too. He's been a good friend, loyal, and protective for 14 years. As long as he's got the will to live, then I'll do what I can to make his life as comfortable as possible.