I'd think very carefully about proofing your swag using this method, and certainly try it out on a piece of similar fabric before committing to the swag itself. Once it's done, it's done, and there's no going back. It will add a substantial amount of weight to what is already a hefty item and will, IMHO, bugger it up. I'd try one of Goatboy's suggestions or the Fabsil, any of which will give you a good standard of proofing without turning your bedroll into a brick. If the results are unsatisfactory for you, the wax remains an option, but I'd definitely suggest trying something else first.