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I understand your predicament quite well as my best friend - also a very keen observer - has been confined to an electric wheelchair for many years now, with muscular dystrophy.
Some years ago I made something quite different to what you suggest. I had a 4" Meade SCT tube assembly lying around and I made a very small isostatic altaz mount for that out of bicycle front wheel bearings and a couple of shelf brackets bought from Ikea for a few dollars. This was then mounted on a lightweight cantilever frame which had two pins that plugged into either side of the back of the wheelchair, at about shoulder height. This held the telescope directly in front of the observer, and the cantilever meant you could lower it to the point the scope was in your lap, or raise it as much as you liked to get a comfortable height for the eyepiece.
At the back of the cantilever was a counterweight to balance the weight of the scope. The result was surprisingly easy to use as the whole thing was nicely balanced - almost no force to move it, yet the scope stayed right where you put it. Also I made an accessory rack that sat on the arm of the wheelchair for eyepieces and a red torch etc.
The nicest part is that being on the wheelchair he could push the scope up out of the way, drive round the observing field for a bit, then pull it back down to have a look anytime, and nothing on the ground to bang into.
I don't have any photos of it but I could sketch it for you; if you can wait a couple of weeks I'll visit him and get some shots for you. It was an interesting exercise and at the time I felt it would be possible to mount an 8" SCT this way. A short refractor (say a 100mm f/7) would also be easy.
One problem you will face is that in a wheelchair your ability to lift things is very limited. You will depend on others to assemble a dob, or anything else that big, and this is going to limit your observing unless you have a permanent observatory to house it too. With a smaller scope cantilevered on the wheelchair my friend was able to assemble it himself - he could observe anytime he wanted - as he still lives on his own.
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