Don't forget that when you get snow tires, Wider is NOT better

The best thing I have found for adding weight are concrete patio pavers (usually 2' x 2' x 2") If you have a bedliner, they work great.
Here's what I do (I have a plastic (drop-in) liner):

Completely clean the bedliner, then put a few 'dots' of silicone adhesive on the raised ridges of the bedliner. Lay the pavers on top of the 'dots', and they will stick in place, so they don't slide around in the back. (be sure to use an outdoor adhesive with good low temp performance)


A Pal of mine uses the traditional 2x4 and Sandbag approach, and it works just as well.

Good Luck, and remember that Nothing beats doing donuts in 4" of new snow

~Paris