in answer to your question, yes you make the nest inside the larsen trap, in the side that you would normally keep the call bird, door shut, that way, the maggies will jump into the "catch" part trying to get to the nest, if the perch is whats holding the spring doors open, make sure you set it really fine
once you have caught a call bird, you must, again by law, make sure it has food, water and shelter, checking daily