Have a old motion sensor light fixture to replace on a job I'm on now. I pulled it to see how it was mounted and to no surprise it was mounted directly to the soffit with no electrical box. I have done these before and always had some issues with trying to properly mount a box in the soffit. It is aluminum soffit on top of old plywood, so at least I have something solid underneath. I want to use a plastic 4" round old work box with the swing out clamps , https://www.platt.com/platt-electri...ork/Carlon/B618R-UPC/product.aspx?zpid=186438, but the screws arent long for the wings to get all the way behind the plywood. Not sure what the thickness of the plywood is (its either 1/2" or 3/4") and the total thickness of the aluminum soffit and underlying plywood is probably close to 1 1/2". The screws on the old work boxes simply arent long enough to go this far in. Has anyone ever replaced these screws with longer ones to get better reach out the wings? I would prefer using one of these http://www.homedepot.com/p/Red-Dot-...Electrical-Box-S215E-R/202202170#.UtqSFdIo5kg but unfortunately there isnt enough wire coming out the soffit to use a surface mount box like this. I am also thinking about maybe using a 1/2" deep pancake box and mounting it directly to the original plywood soffit. This would end up almost flush with the aluminum soffit. What do you guys think?