I use rocks and crawler gears.
Charlie
Surely levelling blocks are cheaper and lighter? Where do you store the rocks? Sedimentary presumably for flatness, or igneous for durability? What sort of proportion of rocks to crawler gears do you carry? Gears for your Mog or just a pile of 404 crawler gears for instance? Once you've driven up a stack of crawler gears would you still use them as spares, or do you carry a second set for that?
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I have thought about a bottle jack between rear tyre and (spreader block to suit) the underneath of the truck bed? But tilting bed slats is a cool solution