I'm looking to make extended seat bags for my bike (like 20L), but I'm not familiar with all the fabric types and looking for some advice. Most bike bags are bombproof stuff, almost canvas, which is not what I want. But I also don't want 0.9oz nylon either. This will be above the rear wheel, so I'm expecting sand and grit to be flung at it often, so a happy medium weight fabric would be ideal. I was checking out http://wiki.backpackinglight.com/MYOG_fabrics_sources and there's just so many options. The dyneema x gridstop looks great but was pretty expensive. I'm thinking coated would be good, and from what I'm reading it sounds like 200 denier is about the weight that would be suitable for this. Anyone have advice? What kind of fabric isn't too expensive, but can handle some good abuse?