Topeak has a new mount that accommodates a variety of saddles. We use the current (now older?) one and it has been rock solid, but the new ISM 3.1 saddle with the vertical rails doesn't work. I'm about to buy the new one; I'll post here if it works.
https://www.topeak.com/...9-TRI-BACKUP-ELITE-2
Also, since we got their bottle cage with the mount, it is now the only cage I recommend to friends, because they stop your bottle falling out by cupping the lower side. Simple in hindsight. I point this out because the new mount also shows a new cage with a rubber ring around it, which appears to keep the bottle tightly held. Great for those small bottles they are using at Kona etc.
https://www.topeak.com/...9-TRI-BACKUP-ELITE-2
Also, since we got their bottle cage with the mount, it is now the only cage I recommend to friends, because they stop your bottle falling out by cupping the lower side. Simple in hindsight. I point this out because the new mount also shows a new cage with a rubber ring around it, which appears to keep the bottle tightly held. Great for those small bottles they are using at Kona etc.