The fixtures generally won't fit between 2 ribs, and most of the jobs I've ever been on are not loaded with other trades that want to make my installations easier or better quality. If a metal bldg has 6 or 8 wallpacks the siding installers are looking at it as a big hassle. We do what Dnkldorf(cool name) said with vinyl siding over wood sheathing installers and it does make a nice finished product. Steel bldgs with metal ribbed siding panels are not as easy for the builder to accomodate us...steel beams at great distance apart with horizontal pieces every 6 feet and blanket insulation don't give you many structural members to fasten to and the siding is not strong enough for screws. Toggles are OK if care is taken.
If you still have a chance to do as Dnkldorf said you can add a mud ring to the 4" sq. box to bring it out flush with the plywood piece, and cut the box opening into it instead of stubbing a cable out. Should work fine.
[This message has been edited by poorboy (edited 07-01-2005).]
