Another thing to think about; Those scissors jacks like posted above and like the ones I use on my TT from a old car; are not as stable when fully extended. And, as you get to the point of max extension you are turning the jack a lot to gain just a little height. When camping on uneven ground I use blocks under the jacks. If you use some nice big 2x8s you have a stable platform and don't have to spend so much time cranking on the jack. On my TT where I store the jacks inside I can keep them well oiled and turn them with my fingers until I get them up to the frame.