Thank you, with the recent photos I've got a much better idea now of what's involved and how different it is from taking a ferry, I'll be bringing a seat pad for use on the saddle and on the floor in Le Shuttle.
I did the cross-channel hovercraft a couple of times, hear they're thinking of bringing it back, I will never ride that again, it was like sitting on a jackhammer in an echo chamber when the sea was choppy, not sure how they think it might compete with Le Shuttle.
Did I understand correctly that it's possible to buy the France to UK ticket on arrival in Calais so can be very flexible about how long the return route ride might take?