Okay! I promised photos of my build, and here they are at last. I was inspired by the various things I saw in this thread and thank you all for sharing what you've done. I hope this helps anyone that might find it useful.
I had six chicks on order so I knew I didn't need a huge heating pad, and I was on a budget.
Upon reading this thread, I purchased
this heating pad, got it, tested it, removed the cover, and cleaned it off (just in case).
I bought a remnant of fleece from JoAnns. I went with any color except red, since I wanted them to be able to "target" the red of the feeder and waterer easily, early on. I've noticed this helps key them in to where to go when they are infants and are still trying to figure out life!
I have scraps of welded fencing left over and decided to use one of those to build the frame. I cut a piece based on the size of the heating pad, with room to make upright "legs" on two sides. After cutting it out, I wrapped all edges with electrical tape. I know chicks have found amazing ways to get into trouble and I didn't want them to find any sharp edges. The frame, bent into approximately the right shape:
The frame, dry-fitted with the heating pad I bought, to make sure of a good fit:
I then cut my fleece to make a sleeve for the heating pad. I did a durable stitch on three sides as I hope to be able to put this through the washing machine when I'm done brooding (for next time, as it were!). The fourth side I did a looser stitch on, because once I want to take the heating pad out, I will need to cut this side open. I decided to stitch it so that no chicks could find a way to crawl into the open end, and to keep everything in place.
Here's the heating pad in its new fleece sleeve:
Next, I attached the heating pad-in-sleeve to the wire frame. I couldn't find bungee cords without HUGE end pieces and I had visions of chicks getting tangled up. I know that in reality this probably doesn't happen, but I am a worry wort!!! So I found some bungee canopy ties that fit PERFECTLY once stretched out over the frame. I secured the heating pad to the frame with three of them, with the heating pad on the INSIDE, BOTTOM of the brooder, so that the chicks have access to it without having access to the wire frame:
These are the ties I used:
I then covered the TOP and sides of the brooder with press-and-seal. I didn't cover the bottom (the inside where the chicks will go for heat) as I wanted them to be able to snuggle against the fleece! I used a bit of packing tape to make sure it was really flattened on the legs of the brooder. I did this so that the chicks didn't have access to any of the wire frame, as I read in this thread about chicks accidentally getting stuck sometimes. Here it is, plastic wrapped (outsides only) to keep everything from becoming soiled as they poop on top:
A view from underneath of the finished brooder heater momma pad, note how the chicks will be able to press against that nice warm soft fleece:
Here it is in the brooder. I have it pinned against one side only; the chicks can exit both front and back. The one side pinned against the tank wall keeps the paper towel in place (at least until they are bigger) so that I can change it and keep things cleaner:
And of course the most important photos... the chicks inside! They LOVE IT! And so do I!