Frankie,
Find a store that sells beds and mattresses. Many of the warehouses use heavy guage sleeves to repackage mattresses. The queen and kingsize are obviously double those bedsizes. Use your charm and a few Loonies to buy one or two. A roll of duct tape to hem the edges and corners and you're set.

ALL synthetic tarps will eventually breakdown under sunlight and simple wear. It's a matter of frequency of use.