Joann,
If you have a wheel extending out from the bottom of the jack "tube" for
lack of a better word, you could very well rip it off when you hit a dip in
the road, etc.
If you would like to add a wheel to the bottom of the jack "tube" I'd
suggest that you purchase one that is made for the task and is designed to
either go on the outside or the inside of the jack "tube" itself. As long
as you have a very strong caster wheel that pivots 360 degrees, has a
ball-bearing plate on top of which is welded a short section of steel tubing
it will be fine to use as you'd like. This short section of steel tubing on
top of the ball-bearing caster plate needs to have a hole drilled through it
horizontally so that you can attach a pin with an attached wire lock that
just swings over the end of the pin. If you visualize the letter 'D' it
would look like that; the straight line of the letter 'D' is the pin and the
half-round portion of the letter 'D' would be the spring wire that flips
over the end of the pin, locking it in place which keeps the rotating caster
wheel on the end of the jack "tube".
For this job I'd prefer a wheel made out of really tough plastic such as
polyurethane rather than plain old rubber. The poly wheel will not mark
surfaces and it will hold up much better over time.
You can find stuff like this at Tractor Supply Company, Northern Tools, etc.
Most likely you will have to have a small custom welding job done for you
once you find out the diameter of the jack "tube". Then you will know by
what you can find at the store whether you need to have a part welded to the
outside or the inside of the rotating steel caster wheel plate.
Simple? ;))
Tom