After much deliberation we have decided to bite the bullet before this trip and try to break in a couple of Brooks saddles which we will use for the ride. These saddles seem to be a "love or hate" item but on balance, after a breaking in period, the general impression is that they become very comfortable, rather like a pair of leather shoes.
The saddles have now been ordered, the B17 Imperial for me and the B17S Imperial for Lorena which is a ladies model and slightly wider. When they arrive I'm going to install them on the VeloTron so that they will have very regular use and hopefully become nice and comfortable before we set off on our trip.
If the worst comes to the worst and this doesn't work out I'll just install the existing perches and put the Brooks saddles down to experience, I'll report back!
Here is the saddle I've ordered: