Not trying to re-invent anything, just use an appropriate design, and sometimes the tried and true really do work best. Other offerings never sit as flush as you would hope, and have even worn holes in water bladders and such. Yes, that was a very long day to find out the 2L of backup water had been dripping down the road behind me. The above is a test piece, as I refine the idea to meet the needs for mounting bicycle luggage.