We currently have an 03 Tiffin Phaeton and briefly had a 99 National Tradewind so I've owed both brands.
I think both are well built and decent quality although there were some things that bugged me with the Tradewind's design (e.g. most ceiling lights only had switch on the light itself (no wall switch) which didn't work well with us since we have young kids (i.e. too short to reach the ceiling), the pull-out sofa bed pretty much went all the way to the wall so you have to move the barrel chair and can't walk by, accessing chassis fuses was quite awkward, hard to access sink if slide was in, etc. Not huge issues but does make me question some of their design. On the other hand, Tiffin labels everything, everything seems well thought out and laid out.
That said, I wouldn't rule either out. I do think that $53k might be too much for a National Seabreeze - the resale on pretty much all Nationals is really bad. I also have some concerns with a unit that might have sat that long.