After our seatpost issue on our spring cycle tour, we switched to our near 30-year old Longstaff tandem. After a few modifications (most notably fitting 32mm tyres), we’ve ridden this tandem exclusively over the summer. One peculiar issue was that after an hour or so riding, there was an irritating clicking sound. We couldn’t quite place it, but it seemed to be associated with a saddle.
We’ve always found it helpful to fit a suspension seatpost on the rear of the tandem, as the stoker can’t always see what’s coming along the road. We have a Cane Creek Thudbuster on the Thorn touring tandem (it was the non-suspension post that snapped) and we had an ancient ITM suspension post on the Longstaff tandem. I can’t personally vouch for the effectiveness of suspension posts, I’m not actually the user - I’m relying on feeback from my stoker on these matters of comfort.