Don't you? There are just a couple of problems, that I fixed on mine (below). The strap comes at 38". I can not be expected to hold onto a bag, I can only be responsible for messenger bags that hold on to me. This requires about 56" of strap (remedied with a few feet of webbing from REI.) I also added a little snap (Snap Design does not include snaps. I'll let you think that over.) to hold my stuff in.
Vinyl bags are the perfect option for weather like this.