You guys are crazy! Box cutters and chisels?! A scrap piece of smooth plywood as backing with a simple clamp to prevent the work piece from moving is all you need If you want to make circular holes or use a drill bit.
Different materials have a learning curve and plastics like plexiglass, lexan, hdpe, and ldpe will crack when cold. The trick is heating it up till it’s got just a little bit of give to it. You can use a hair dryer or just put the whole piece in a oven and set to low.
Brad point bits are best for smooth clean holes as they eat away the material more evenly. But still use a scrap backing when applying force.
When using a hole saw first get the guide bit in then run it in reverse. That way the heat from the friction of the teeth are what’s cutting the plastic and it will come out smooth.
I will never recommend heating elements glued or screwed against plastic. Glass is better and safer. It is inert, water proof, and most important of all it is crystal clear so you can actively observe your charges. It’s huge draw back is the weight and pro ness to shattering, so I never go over 30 gal fish tank size.
Aluminum screen is far to large. It does work for almost all of them but not B germanica sized ones!