Chris,imaging you have a flat tyre or let the air out of your van tyre,then look at the gap between the axle/chassis plate and the road I do not know of any bottle jack that will fit underneath also I do not think they have a wide enough base/footprint to be safe whilst lifting,I think the only safe way of jacking with a bottle type jack are the ones that fit onto a bracket fitted to the chassis.A trolley jack will slide under the plate and lift with few problems and you will be using a pumping action which is far easier than trying to turn a winding handle of a scissor jack,Just a thought ask a pro,ask the advice of a mobile caravan servicer.I hope you find a way that suites you before you trip.