1 word: Goretex.
I have a Goretex parka that is the bomb. You'd want Goretex trousers as well. I even have Goretex boots. Smother yourself in Goretex. Though, it's too late for you to set up this system for Monday night. And it is costly. https://www.ebay.com/b/Military-Gortex-Jacket/57988/bn_7023410187
Alternative, if you can find it: An Army surplus poncho. They are bigger and heavier weight than customary ponchos. They do a good job. There is an Army/Navy store on Transit Road near Main Street, maybe they have them in stock.