If you are going to add weight to the truck, I would use a couple water/chemical, tanks that farmers use.
A local farmer (see if any are going to pull) might let you borrow/rent a couple empty tanks. Then your local fire department might help you fill them, (might just have to make a donation to them). Then after the pull they might want the water for the trucks, the farmer might need it, or you can find somewhere to dump it, as long as its not contaminated.
Also a scrap yard might loan you some weight. You might just have to cover you and the truck with the company name.
Hope this helps.
Good luck