Hopefully this link will get ya there..... it's an 8 part video series and the end of part #6 and part #7 is where they have most of the info on snaring....
http://wildlifepronetwork.ning.com/video/video/show?id=1998073%3AVideo%3A168&context=user
Edit..... part 2 shows him setting a crawl under.
Thank you Stu
The video helps a lot.