I wouldn't use anything less that 3" of conc. w/4"x4' welded wire mesh imbedded in it and cut an inch short on each side so it doesn't come to the edges. Allow to cure for 21days and you will be ready to go. Be sure to wet the existing conc and make sure it it clean to get the best bond. I would even go so far as to spall off the top surface of the existing conc. to allow a better adhesion.
in simple mans terms

anywho,no amount of dinkin' with wedges and such have produced anything that I'm comfortable with,...might try some cinder blocks,maybe I can get a couple rows of them in flat enough spots to get it done;I'm thinking 10 to start,two rows of 2 on each end with 2 in the center,some 2x6's across with a plywood base...might be on hold now for awhile..got that spring turkey hunting thing I need to do for the next month or so