Considering an HTT. Where do I start my research?

FWIW, you can get an idea of what used trailers should go for at Nada Guides, don't bother using all the options, just go with the base price. In general, used models at dealers are way over priced. Expect to get a new one for roughly 25-30% off sticker.

Again, use rvdirect for valid prices if you go new.