Is it possible to finance a $23K trailer for 180 months?

8.49% is high, interest rates are at an all time low. You might be better with a home equity loan and pay cash for the trailer, your carrying costs will be a lot less.

An RV is a depreciating asset just like a vehicle, the fact that it will be worth less as it ages is not a reason not to finance. If you put 20% down, chances are good that you'll never be upside down on the loan, or, put $0 down and if you have to sell early pony up the difference then.