Tons of them on Amazon Tony, take your pick. https://www.amazon.co.uk/packing-cubes-travel/s?k=packing+cubes+for+travel
When my Mrs and I did our France-Spain-Portugal tour we had a right old stand off about the type of baggage we were going to use. I favoured the above mentioned liners. She favoured completely unstructured thin lightweight hold-all’s that you can get on the web. She had a point. They’re thin, really thin, really light weight so they take whatever you shove into them but when put into a top box or even a pannier they adapt to its shape, no wasted space. They have straps so you can carry them into a hotel and they’re cheap as chips. You can get them in Ducati red or black, whatever suits. I’ll get the Mrs to look it up tomorrow, see if I can post up a link.
I went with the Ducati bags, as they weren’t that expensive in the grand scheme of things. The great thing with them is that no matter what you put in them, as long as they zip up, they’ll always fit in the panniers straight away, with no faffing about trying to manipulate them in to the panniers.
I like using soft panniers so I can't comment on hard pannier liners but I can highly recommend packing cubes. My wife converted me for a long trip we did and they made life so easy. We used Sea to Summit. She did a short blog post here that shows the cubes: Phil and Dee's Travels: Packing my Pannier (inbetweendogs.blogspot.com) Also, I am a fan of dry bags and we used a 30 litre one inside each pannier.
Actually you are right, mine are Eagle Creek as well. That explains why I can't find them on Sea to Summit!!
Trust me Tony. Even if you just have one A4 size one for your spare riding gear, another for your off bike gear, tee shirts etc and a couple of small ones for your smalls you find it’s a lot easier to keep track of everything and pack quicker.
I've got them. They are a good fit in the panniers, you can always stuff something in the little gaps that are left. Very good value for money and decent quality. Perfect for carrying the things you need into the hotel. I'm very happy with them.
But man, I'm nothing like as seriously 'organised' as you are and prefer to remain more Avant Garde like the Sahara Sunset kid. You know what I mean?
Like Chris ( @Twin4me ), I'm a great fan of packing cubes and also like Chris I'm well organised - which will come as no surprise to you Tony (@TonyMNo1 )
I see there are fans of hard cases and fans of soft bags here. I've not got great touring experience to lecture by, but the bike came with the hard cases and Id think the security they give enabling me to wander off away from the bike gives peace of mind. If I had soft bags Id be worried they'd get stolen or Id have to stay in sight of the bike all the time. Guess soft bags works well for real adventure riders out in the wilds, no one around anyway and if you drop the bike they don't damage easy. Smash a hard case and its going to be expensive to replace.
I agree if you are riding off road then soft bags are best. Most of the parts are available separately for the panniers so you don’t need to replace the whole unit, (which I know from experience makes it cheaper!)
Just a quick note on security with soft bags, yes I agree you have to be careful but I have not had any issues yet. I just try to make it awkward for the opportunist - I carry several small wire ropes and small padlocks that I use if need be. I make sure I am not away from my bike for too long and when I do, leave it in a place with people about. I also use these wire ropes (3 - 4 mm in diameter and plastic coated) for my panniers, dry bag, tank bag, helmet and bike gear if I have changed out of it in a hot country. I also wire things together in my tent if I think its a bit dodgy. Pacsafe also make a wire rope that you can adjust and padlock - called a Wrapsafe Adjustable Cable Lock - quite good if you can't get your own made.