On the issue of a homemade RHP, there is a guy with a YouTube channel (Animals at Home), that posts here sometimes. He had an instructional on building an RHP by sandwiching typical heat cable between two pieces of peg board. Here's a link: https://www.animalsathome.ca/reptile...t-heat-panels/
I've never tried it, and never would. I buy all my RHPs from Pro Products, now and forever. Yeah, Bob is pricey, but the quality and reliability is priceless.