Totaled my fifth wheel, how to work with insurance adjuster

What you paid for it is not part of the equation. Does not matter. Only question is what does it cost to replace it. I would go to the dealer you bought it from (or another dealer), ask for a letter on what they would want, if they had it. Go to RV trader. find values. Give those to the insurance company. It is not your responsibility to have to negotiate down on asking price, on a replacement unit. But do your homework. Another idea hire an RV appraiser, for a few hundred bucks.