Can only tell you that we had a ROO 23SS and our camping buddies had a Shamrock 19 and while we had only one minor leak while driving through a monsoon, they had one in their front bunk. Both were '07 models with the same seal design. That has been improved since. FR did supply new bunkend and decking material. True that ALL HTTs MAY, MAY leak. That is also true of ALL RVs in general. The nature of the beast just means that it's a possibility. Just as "the best" manufacturer can and does turn out a lemon from time to time.
Re the 2 vs 3 bunk model, if you have a regular need for the 3rd bed, suggest you go for that one now. Looking at an online listing for the Coachman, notice that it does not have a dinette AND sofa, which the Shamrock has. The Coachman offers more floorspace, it appears. Unless you have the need for that third bunk, I think you'd be happier having the sofa. You can open it up for occasional guests, but doubt you'd want to make that a regular occurrence. Also, the Shammie is 2 years newer model with likely better sealing system. Only you can decide which one really meets your needs, but we're on our second Rockwood - same as Flagstaff/Shamrock - and are very pleased with both. No problems. Good luck.
