G'day Tara,

The simple answer is no.  In order for a bag to be waterproofed the fabric has to undergo particular treatments at the manufacturing stage, before it's turned into a bag, and there needs to be specialised zips, etc.
We have a video on how to re-waterproof your tent, in theory you could potentially use these products to try an add some level or waterproofing to the bag, but it would be a big investment in the products for something that may not actually be super effective.
I would personally just be getting a good quality tarp to wrap it in, & a few short tie down straps to keep it all together - a cheaper, easier, and hassle free option.