BMW MOA co-founder
I found a new 35 litre Harro Elefantenboy on e-Bay a couple of years ago. It's completely waterproof using old fashioned rubberized canvas construction with real leather straps and steel buckles. It's amost infinitely adjustable in size from small to huge, and zips off the mounting base for easy filling of the tank. The only concession to modern manufacture is a bit of velcro to close the map compartment. It looks like it could have been made in the 50's.
It's a quality item and is a perfect complement to my R50.
I posted a picture of it on my bike here: