A friend set me up with 16 plates from a rusted out weightlifting machine. Not sure how much they each weigh, but assuming 10#s each it would add 160#s. Started with a piece of all thread in the trailer hitch hole and one plate. Added a couple of pieces of flat stock to make a shelf for a second stack. Tied the front stack to the top of the rear frame plate with a piece of stock with a 90 bend on the end. Those pieces are long enough to tie the rear stack in too. Whole thing seems pretty stable so far. Hopefully I don’t blow out a tire!