Both of my hoods are plastic, with guide lines that CAN be used to make cut outs for your filter and heater.* I found them to be too big for the equipment I had, so I just measured how big a cutout I needed, marked it on the hood,* and sawed the hood down to the depth needed.* Then using a straight edge (ruler) and a box cutter, I scored a straight line, multiple times, between the two cuts, and using pliers, snapped the piece off.* No excess hole area to worry about.* Everything fits snuggly, and it wasn't much work at all.* Good Luck!* *
