Yep I made a similar one. Seems to work fairly well. I used a narrower, longer stuff sack to make more clearance for the rear tire. All in I think it was ~$45 in materials and weight IIRC was ~110g, excluding the Valais. With all lightweight gear I'm sure it's not forever-proof but seems durable enough to survive me throwing the bike through manzanita and chamise. I can't feel it flopping at all while riding, but haven't watched myself ride so can't know exactly how much it might sway.
Either way I say it's an affordable and light option that should be moderately durable.