O.K. I'm just spit-ballin' here, so bear with me. My first suggestion is to sell this bearded dragon enclosure to someone that has a bearded dragon and put the money toward a PVC enclosure. This enclosure is too open, and it won't hold heat or humidity. You can modify it to make it work. Lots of people do, but if you want a nice enclosure for a ball python. It's not a great start.
This enclosure is built for a heat lamp of some sort, not a RHP. Beyond the problem of having nothing to attach the RHP to, the 80 watt RHP you want to use is too long. It'll cover half the enclosure, so half your enclosure is going to be hotspot. Usually you aim for a third. Makes it tough to create a proper gradient.
Assuming, for whatever reason, that you're determined to give it a go. I'd go with Wanik4's suggestion above. I'd buy a piece of 1/2" PVC sheet. Cut it to fit snugly over the screen and screw the RHP, through the screen, to the PVC sheet. The PVC should also help hold in humidity. I'd cover the sides with foam board as well for insulation and to make your BP feel more secure. I don't know if securing the RHP to the side would work. I'd be worried my BP would rest against it and get a burn.
This is just what I came off the top of my head. Take 'em for what they're worth and best o' luck to you.