Thanks for all the replies. I ended up using the UTH. I was GOING to stick with the human heat pad but I am leaving for about a week and I just did not feel ok with leaving it alone that long even though I am sure it would have been fine.
Anyway, I have a small bin with a UTH on the side. I put the small bin inside a large bin. Then I stuffed an old blanket in the open spaces between the small and large bin. (except for the side with the UTH). Then I wrapped the entire large bin up in an old sleeping bag. Then sat the Large bin lid lightly on top (air can pass through to the smaller bind vent hole). It looks like a bunker, but it works hahaha.
thanks again everyone.
Anyway, I have a small bin with a UTH on the side. I put the small bin inside a large bin. Then I stuffed an old blanket in the open spaces between the small and large bin. (except for the side with the UTH). Then I wrapped the entire large bin up in an old sleeping bag. Then sat the Large bin lid lightly on top (air can pass through to the smaller bind vent hole). It looks like a bunker, but it works hahaha.
thanks again everyone.