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I also built one. Haven't seen the pictures of the one Tman122 built but i made a box 25"x25" and bought 2 replacement grill racks for the towel shelf. Put in a couple 100 watt drop lamps for use as heaters and then lined the whole thing with Reflectix insulation and tada instant towel warmer. I did change out the 100 watt drop lamps out with a 500 Watt halogen lamp because the drop lamps were just not heating the towels to our liking. That halogen lamp definately does the trick.
I have one of the store bought ones. You can see it in my thread in the "show us your hot tub" section. We like it, but you need to turn it on about 15 mins before you plan to get out so the towels will be nice and toasty.http://www.whatsthebest-hottub.com/forum/index.php/topic,16194.0.html