I would NOT recommend Longmarch tires (supposed to be the same thing as Hankook). We went through some rotten times trying to figure out why our coach was shaking so badly. Turns out, of six brand new tires, not ONE of them was in round. We returned them and went with Toyos and they are doing fine.
Our Winnebago had the same 16.5" "special order" tires. We ended up getting a tire that is not made any more for it (sadly, because it was a good tire). I hope you don't have trouble getting tires for yours!