X-chocks alone is a bad idea because the TT can still move and the chocks will just roll right out. Have seen it happen on sloping ground before. Okay to add after you've done all the other "right stuff" first.
Never been on ground quite that bad but I would think some single length 2x6 or 2x8 planks under the tires on each and long enough to run past on front and rear of tires for the blocks would be a good idea. Will spread out the load per square inch. Then larger heavy duty blocks on each wheel on the planks.
I'd watch what you use to put under the tongue jack. I had the short 8x8" blocks under our tongue jack sink into soft ground once and the TT slipped sideways and off the blocks under the jack. Not exactly an easy job to get the jack pad back onto some blocks. Good thing I had the chains attached. I'd suggest using a much wider base under the tongue jack in both directions like say 2' x2' (or even larger) at the base and in a pyramid shape.
I would think some stabilizer struts added to the stabilizer jacks in a fore/aft and side-side direction would also help. And larger pads under the stab jacks too.
