Or a big wash-basin full of "pickled sand". Whatever you put in the back of a kickup TIE IT DOWN WELL. You do NOT want it coming through the back window of the cab if you get "out of shape".
On my 57 Fargo I bolted a roughly 3X4 foot 1/2 inch steel plate under the box behind the axle. That was just to get traction in the SUMMER!!!.
On my ranger it's got a heavy fiberglass cap and a box liner - I've had no traction issues so far with 205-70/15 graspics - should be better yet with 235-70/16 Hak R2s on all 4 corners.