NikWax: great waterproofing for...everything!
I just applied NikWax products to the OYB Bag and it seems to work well!
I haven't used it yet, though, much less in any rainstorms, but it sure seems to repel water!
I got their "Cotton Proof" product and painted it onto the canvas portion of the bag in a 6-1 dilution (their suggestion for tents, it looks like, it was a bit hard to follow their instructions) with a small brush. It painted on white then dried invisible and seems VERY waterproof! It smells a bit like Elmer's Glue.
If I put the bag under a water faucet all the water simply flows off. With an untreated bag, the canvas immediately is saturated.
(Now, canvas is famous for saturating then swelling shut to create a barrier that only gets wet but not "flow-thru" wet. This can keep the interior of a tent dry---while the tent fabric itself is wet---but doesn't work so hot with packs.)
I also bought their "Leather Conditioner" which a reseller said would work for the painted/coated leather part of the bag. It also seems to be repelling water very well.
The bag will never be waterproof like a rubber drybag, but, man, the treatment sure seems to work and would doubtless help keep things inside much drier.
Here's a link to get your own supply: http://www.greenboatstuff.com. Tell em I sent ya!
I'll paint on an initial coating to any OYB Luggage item for $5. Click your item ordering button, then also click this button: