Build a small enclosure around it to keep the wind off it and trap a bit of the lost heat. Definitely don't want any rain in your insulation either. Around the outside of the smoker hot water tank wrap, mineral wool board with liner, wool duct wrap, or similar items should all work. Grab a roll of tape for it and tape all the corners edges, and openings you have to cut. Seal it up nice. Just make sure everything has temperature rating suitable to where you'll apply it.