Making waxed cotton

Does anyone have experiance waxing cotton or have a formula to do so? I found a few recipes online but thought with all the knowledge here this is the place to go. Filson makes great stuff but I have a few old carrhart coats that have become sponges & still have life in them if not worn in the rain. So I figured I'd try to make poormans Filson out of them! Any ideas or suggestion? Thanks for all the great info I find here!