If you want to cook at 250F, you are going to have to help the thighs along with rendering, many folks use the part of the Pickled Pig method which scrapes the fat off the skin and then replaces it. Some folks swear by mayonnaise as a coating.
My preference is to cook a lot hotter, at least 375F and up to 450F.
Whip It Off, Chambers!
"perhaps...but then again...maybe not..."