I would use the $12,000 to pay off the trailer (if needed) and then when it comes time to trade in, anything that you get over $4,000 is bonus money! Chances are that if you sold the RV to the insurance company, they would do a quick repair, like change the leaking roof vents (that you already did) and sell it for around $5,000 - $8,000.
No reason I would not buy a used RV that has bad hail damage. As long as it is not leaking rain, keep the $12,000 and the RV, enjoy it for another 5-6 years, then you can probably get $8,000 for it in 2020.
Fred.