Must agree with Flatfour, never had any issues in the rain. Especially with the large bag. Never found any issue with water proof covers.
As long as tightened correctly.
...and it is the tightening of the snug-string on the covers that is the issue. The first time I put the cover on mine, I left the release toggle fastened to the press-stud on the bag and covered by the rain-cover. Next fuel stop and the cover had to come off to get the bag off and away it flew in a storm. Oh, how I laughed.
So, not being one to make the same mistake twice in one day, when I re-fitted it I undid the press-stud and left the release toggle out of the cover. Smart thinking eh?
Next fuel stop and the release toggle was nowhere to be found. So, off with the cover again and still no release toggle. Eventually, having moved bike to the side of the pumps and stripped off gloves and helmet so we could investigate further, we could 'just' see the toggle which had disappeared under the bag never to be seen again and because the bag fits so snugly to the tank, it was out off with the seat and out with the old wire coat-hanger I have taken on tour for the last 30 years and never needed...
Eventually we managed to fish out the release toggle, take the bag off and fill up. Oh, how we laughed at all the fun. I now have a second release string tied to the release pin and fastened permanently to one of the strap loops and just as well as the toggle disappeared under the tank again last week when I put the rain cover on.
All in, too bloody fiddly by fa in the rain, but great in the dry.
And yes, I do have a big tank bag Richard, a Touratech one (complete with excellent rain cover with clear top and velcro-on map pocket to boot) from my old R1150 GS days and despite the difference in tank designs, it works fine on the K and having a 'sticky' bottom it doesn't even need straps to hold it in place (I used it unsecured all the way to Oulton Park
) but it is too big for my needs when I have the Cases on.
