I said on the 2019 thread that I had bought a [slightly too big] Tourtecs air cushion. Yesterday I tested it.
In a roughly eight-hour 320-mile ride on all kinds of roads I probably spent about 20 minutes off the bike, though half an hour was spent sat stationary on the bike talking to someone at a petrol station. After that I had another 30 mile trip.
I am certain that I would be in agony after a journey of that length. Even had it been a normal day out, one with a several-hour gap in the middle. But I was not.
It is not that I did not feel anything, just that the discomfort was so minor that now I cannot remember it. Which is not something I would normally say. The pain from long rides will normally last the rest of the night and the memory hold for several days.
More experience with it is needed before I can say it has solved my problems, but my initial reaction is quite positive. (And with new tyres and okay weather the last 80 miles on rural B-roads (minor roads) was a super enjoyable ride.)