Excuse the not so focused pictures... and the fact I kind of took pictures of different sides of the ones I was making haha.
So in the spring I needed a couple more fermwraps so I ordered two online at around $30/each (they're even more at some retailers). After a week my order still hadn't shipped (apparently they were out of stock and mistakenly didn't contact me but thought they had)... I was getting antsy and searched around on the major forums to see if anyone had ever made their own or had any reasonably priced non-light bulb alternatives. I was surprised to find nothing here (though maybe I didn't look hard enough?). They looked pretty simple to make so I figured they must have a huge markup unless that heating tape was expensive.
I eventually found a "homemade fermwrap" thread on the BN forms where someone else was looking for cheap alternative. It was only 7 posts long with two people mostly discussing a website malware issue. I'd expect such a thread to be more popular! A website one guy posted had a tutorial on making something that looked exactly like the Fermwrap, with the same parts and everything.
Apparently people make these in the Herpetology community as they need to heat cages for the snakes and reptiles they keep as pets. You can even wire them in parallel.
The heat tape is called "Flexwatt" and comes in various sizes: 3" (10 watts per foot), 4" (8W), 11" (20W) and 17" (20W). The commerical Fermwraps we see are made from approximately 2 feet/panels of the 11" Flexwatt.
Some Flexwatt comes in panels has nifty little cut here lines about every foot. (Each panel is 12.5" to give room for the wide cut here area, check end of thread to see completed comparison pic). The retailer I bought from recently switched to the non-panelized stuff. With the non-panelized, you just cut to any length in the clear plastic, between the black heating elements. Don't cut through the black elements! I used a yard stick and boxcutter to cut mine nice and straight, scissors would also work cut through it fine if you have a steady hand.
So, let's get started:
Chop the end off a standard extension cord you can find at Walmart for around a $1.
Pull apart the two wires about 12 inches. You might need a knife to make a small incision between the two wires to make it easier to pull.
Then, cut about 1/4" of the insulation off each wire with cutters, or a sharp knife.
Insert one wire into a metal connector. You can simply put the bare wire into the hole and crimp it closed with pliers. I pushed the brown cord a little ways in so it was snug in there before I crimped.
Slide the Flexwatt into the metal connector's slot so it's teeth align with the shiny silver metal strip. Fold the connector piece sticking up down and into the plastic. You can hear the teeth bite into the plastic and touch metal. Crimp it in place with pliers (not pictured). Repeat on the other side with the other one.