Whilst I appreciate some people may have a "grounding" issue and when it does happen them its obviously annoying or potentially damaging. Using a good "Banksman" should make the driver aware of the issue before it actually occurs, and prevention is always better than cure.
Hower there will be a few people whose access does present this problem, and they need a solution to prevent grounding.
My immediate impression is the castor as illustrated rather compromises the foot of the steady. Secondly by making the steady the fixing point for the caster, means if it does come into contact with the road/driveway and becasue of the angles of the surfaces, it will apply a very considerable force to the steady probably far in excess of the the steadys normal expected loads and my damage the caravans structure.
And using a castor with such a small diameter, the wheel is likely to get stuck and drag with relatively small stones.
I'm sure a well placed short scaffold board or ramp would be a better solution. Or consider a caravan mover or plenty of helpers to manually push the caravan.