Adding Weight or ballast in the trunk.

I use a big old craftsman open toolbox, bolted thru the floor, and one frame rail. Two feet long, one foot wide, one foot deep, i know i can get almost a hundred pounds in it. Take a padlock off, open the lid, add or subtract whatever.

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Put it over the rear axle to just add weight. Farthest back you can put it on the passenger side, to help traction.
Edit, ignore the splash of sunlight, its not in the trunk at the moment.