Stuart,
I use a Dry Bag ( which is normally used for cloths when sailing )
Likewise (as a white water kayaker I do have a couple to choose from) but my choice every time would be for an Overboard bag, cheaper than the boot bag , and takes 130 litres, and I can vouch that it is totally waterproof , even on (thankfully brief) total immersion.
https://www.over-board.co.uk/waterproof-ninja-duffel-bag-130ltr-black.html
