Those are very good video's, CN!
Loved that action vid on the grasmower...hahahaha
To give you a tip on your construction:
The innertube and outertubes are ok, but you could try to make one endbouching bold on the outside. (No threading)
Use a copper ring to make it airtide.
So, when you mount it all together with help of those endboucing, which you screw on the innertube, you tight it all up.