My brother once made some wax signs for his store they were cheaper than laminated paper and lasted for months in the snow and rain. For a tarp I think you would need a very oily wax (more malleable and less prone to cracking and crumbling off). Something like toilet seal wax I think would be best. I once made a lip balm out of pig lard and wax thatès what you need fat and wax mixed. I doubt you can make it for less than the plastic stuff though.
Diversified Food forest maker . Fill every niche and you'll have less weeds (the weeds are the crop too). Fruit, greens, wild harvest, and nuts as staple. Food processing and preservation are key to self self-sufficiency. Never eat a plant without posetive identification and/or consulting an expert.
Stop it! You're embarassing me! And you are embarrassing this tiny ad!