: Has anyone here ever taken a truck or tractor inner tube
: and put a stretcher frame in it to shape a Kayak-type floating
: device?

Whatever it is it ain't a "kayak".
Yet it sounds like a good idea if you want to float but don't want to go anywhere. It will have poor hydrodynamics, ( that means it will paddle like a pig). It will sit high on the water and get pushed around by every gust of wind which is a saftey concern all by itself. Whatever you paddle has to have the ability to make some headway against the wind in case that is the direction of home.