and dropped off a Sea to Summit Evac dry bag.
£15 seems bargain too though it took a couple of weeks to turn up....
https://www.sportpursuit.com/catalog/pr ... a49f2881a8
20L, works perfectly as a liner to my (already waterproof) Carradice saddlebag.
I'm planning on using the Carradice instead of the Ortlieb seatpack on my Southampton to Ludlow ride in a few weeks, mainly due to it's phenomenal stability ( sits on a small frame/rack) and ease of packing.
The Evac is sold as waterproof but rather than a valve, has an air permeable base, so chuck the quilt/warm jacket/liner/pyjama's/teddy in the Evac, fold the rolltop a few turns then press/sit on it and evacuate the air from it.
It does seem to slowly reinflate somewhat, but it takes longer than getting it in the Carradice and packing other shizz on top. And it can be compressed in the tent in inclement weather, where as the Ortlieb is a faff to get on & off the bike/covered in sheep sh!t so needs filling in situ.