I am setting up more hives and strongly believe having a oil trap for the bottom board is a necessity to control SHB. Rather than order them, this time I would like to build my own. However, my carpentry skills leave a lot to be desired. I have seen Rusty's IPM design and others in the thread on this site and have a question. I have found it impossible to find a ready made aluminum try that will fit, and when I try to make one out of sheet metal, I can't seem to prevent getting waves along the side walls. The only way I think I can compensate for this is to dado into the sidewalls...but I'm worried about strength. I could use 2x4, but that would create a lip around the edges where beetles could run around without falling into the pit. I've seen some designs on here that do use 2x4s and have a ledge that can handle the curved corners of the store bought aluminum pans.
My question is, how much do ledges on the bottom board change the effectiveness of the trap? I'd love to not have to make my own trays, but don't want to have SHB laying eggs at the back of the board in an area not covered by the oil.