They suggest elevating the pallets off the ground with stones/bricks however I have been either been placing two of them flat on the ground facing each other or elevated on top of small logs (they will last longer since not in contact with wet ground). I ensure the ends with the pallet forks openings are facing each other (provides rabbit runs), separate the pallets by about 2/3 length of the pallets and place one on top to cover gap between the two, place your salt in the gap (where legal). I had large sheets of thick rubber that I cut and placed on top of pallets that protects the salt if you use it as well as helps to preserve the pallets, I then cover them in a wide area with brush. If you have rabbits in the area, they will immediately start using.
I have also made some out of cinder blocks, form a circle with some of the openings facing outwards, lay a roof on top and then brush. You can essentially utilze anything availble to provide structure and a base. Attached is a link from Indiana DNR that further explains different practices;
https://www.in.gov/dnr/fishwild/files/Wildlife_Brushpile_Jobsheet.pdf 
