How are you taking basking temps? You need an infrared gun to get accurate readings. Your temps might not even be as hot as you think.

UV isn't necessary. I know you said you are going to switch enclosures, but that exoterra tank is wrong for a savvy.

I would bet bet once you get his temps up he will begin eating better. Are you dusting food items with supps?

Try a warm bath for hydration and helping any possible impaction.