Travel trailer Trade-in - what to do?

Went to my local RV Dealer yesterday, to get trade in value of camper.mWe have purchased our last 2 campers from them. I have a 2011 Passport Grand Touring , power hitch, power jacks, power awning, dvd,cd, flat screen tv, outside speakers, attached grill,1 large slide, bunk beds, queen bed, U shaped dinette. This was a special unit back in 2011. Total price $33,000. Had to put down payment $8,000. Total financed $26,000. Now I am told that in 4 yrs, my unit has depreciated so much, that trade in value is in $13,900. Dealership advises per NADA guide, not worth anymore. Apparently they could only sell unit for $20,000. I advised salesperson(whom sold us our last unit) that I am trying to buy new smaller unit, with little money out of pocket. The unit I was interested in buying from them was $18,000, discounted from $24,000. I was told I would need $8,000 out of pocket . I was told that since I was buying an already discounted unit, price for trade in probably couldn't chage much. I was told if I was purchasing $100,000 motor home, that would probably payoff my camper. I was told owner is a business man, and that rv deals are not the same as purchasing/trade in of cars. My payoff of my unit is $22,000. Sales person asked me how much available cash I could put down a new unit. I asked her if they take credit cards, told due to fees, they only would let me charge $1,000. I overheard another salesperson tell a customer that you need to put 10% down. Do most dealerships require customers to have a cash down payment. So, at this point, my unit has lost $19,100 in 4 yrs. Suggestions?.