Welcome Doug,
You're correct, the Zeppelin is no longer made (aka 'an orphan'); and if memory serves me correctly, I think 2007 was the last year & it then was replaced by the Keystone Passport line.
Buying 'used' can be a good choice for first-time owners, especially if you're unsure that your family will enjoy camping. A Lite/Ultra-Lite trailer (one that's truly light-weight) would typically be the best match for a 1/2 ton truck.
If you'll do a *search* on the forums, you'll find some posts about the Zeppelin from last year.
In reference to the roof leak -- it was caulked (& supposedly stopped), but the water damage was never inspected or repaired... correct?? If that's the case, then it's my opinion [only worth 2 cents
], I'd steer clear of any trailer with obvious water damage, regardless of the manufacturer. Odds are there's more involved than just the 'now crunchy' sub-floor; there's also the potential for mold within the roof, walls & floor. All things considered, it could turn into a 'very costly' purchase.
Spring will be here soon... good/used trailers will be more plentiful.
Good luck, and hope this helps.
Terri [& DH Kevin]