My solution to the insulation issue was to make a quilt to go snugly under my HH. I used #400 thinsulate (about 0.5" thick) for insulation. Getting the "snugly" part right was tricky as you're working with a surface that's curved around multiple centers but with persistence I've got it right twice now, once on my HH and once on my wife's HH. Sure, it's more bulky than putting a pad inside. The bulk is countered by the ease of set up and not having to wake up every hour to get myself back on a pad that's no longer underneath me.
I tried HH's undercover and foam pad system and consider it the worst $100 I've ever spent. The undercover is a pain to set up properly and maintain in place. The foam pad is way too flimsy for the intended use. If you've got one and have duct taped the holes you've put in it, consider replacing the pad with headliner cloth like that used to insulate curtains using the original as a pattern. Headliner cloth can be found in most larger fabric stores and consists of nylon fabric on which a nylon foam has been formed. It's tough stuff and much better suited for the application. I used it until I decided that a closely fitted underquilt was the ultimate solution.
I suggested headliner cloth to HH but got a "no thanks" reply, which, considering how poor their product is, makes me wonder what motivates them.