We wanted a shorter 5th wheel too. We ended up with a 30 footer because the living/kitchen space in the 25 footers just seemed too cramped. Depending on the exact floor plan some of the 25 footers were better than others, but none really felt good to us.
If you decide to consider buying new, you might try looking at the Winnebago Minnie Plus line. There are three floor plans. The 25RKS comes in at just over 27ft total length (and does have a stand-up bedroom). The 27RLTS (this is the one we have) and the 27REOK both come in at just under 30 ft total length. I would guess you would not find any of these used just yet as it was a new line for the 2018 model year.