Plus one on the microwave I have the smallest one I could find tucked in the Linen cabinet in the "Shave Den" I have it adjusted power wise to get the exact temp I want every time at exactly 1 minute...
I tried the crock-pot/rice cooker idea but it takes to long to get them heated up... Same with the actual towel steamer they are designed more for a barber shop type operation where it is turned on in the morning and used throughout the day....
The other idea I tried was a heavy crock that I put the towels in, then poured boiling water on at the start of my shower, again the time, and the going up and down the stairs didn't work for me... YMMV

This all was observed with huge eye-rolling from the SWMBO !!!!!