Finally got around to insulating my hot water tank today. I ended up using an 8"(biggest dia. home depot had in stock) insulated duct sleeve:
Cut a piece off about 24" long to allow extra on each end of the tank to wrap and tape, then sliced the foil exterior shell down the middle(didn't have to slice the insulation itself since it was already cut lengthwise) with some patience slide it in past the cold water line and behind the tank. Then laid it over and tucked it in under the front side. I used silver foil ducting seam sealer tape to tape the ends closed. I cut a few more small pieces and tucked in behind under the tank where it goes through the wall of the trailer to the outside controls. I'm pretty happy with how it came out, besides it looking like jiffypop popcorn ready to explode
It will do for now and easily removable if I come across a better insulator.
Here is a pic, let me know if you have any other suggestions now that you see what I'm working with.