Bank-owned horse trailers can be purchased from auctions. When a vehicle of any kind is repossessed, the bank or loaner can choose to do what they please with it. They may sell it to an individual party or to an auction.
There are companies dedicated to purchasing repossessed vehicles and reselling them to the public. These resells usually include auctions where buyers can bid against each other for the vehicle.
CrankyApe is a notable auction website that deals with bank-owned recreational vehicles. Their website hosts auctions where members can bid on trailers, campers and RVs without concerns for hidden fees or price reserves.