You are likely in the ballpark about the value - depending on the time of year and getting the right buyer. I would consider something like this a semi-liquid asset - it's almost like cash you can have fun with.
Take the youngsters camping and have some fun. The thing won't depreciate much more. And if it does - if you wait one year to sell it and have just 4 good camping trips - will the memories or the $4k be worth more to you?
But if you need the money, sell it, buy some thermarests and a tent and go have fun. It doesn't matter how you do it - just do it.