Lighting, Light Fixtures, Ceiling and Exhaust Fans - Acceptable Mounting Box for Exterior Light

I want to mount several exterior lights (on outside wall surface) for new construction work. I intend to mount the lights on Builder's Edge type mounting boxes. The lights will be small, lightwight fixtures. Can I use a rectangular 2 x 4 adjustable plastic box such as shown in the link below. The box will be in an exterior wall

http://www.carlon.com/sd-cgi/hsrun.hse/CarlonCatalog/ProductCatalog/ProductCatalog.hjx;flag=restart;start=ProductCatalog.HsLogin.run?FromSite=carlon&CatalogObjectId=88

Is such a box acceptable, or do I need a) a weatherproof box, or b) a ceiling box made for mounting fixtures.

using a would present mounting problems since they're made to be to flush mounted. Both would seem to cause problems with respect to ensuring that the face of box is flush with exterior wall.

Thanks.

You could try something like this with the box built in.

http://www.aifittings.com/whnew45.htm

You may want to check out other products from the same company.

http://www.aifittings.com/whnew13.htm

Most lighting fixtures mount best on round boxes. 2x4 boxes usually work OK too - but not always.

I'd use a 3" round fixture box - set far enough forward on the stud that it flushes up with the finished siding material. If you're using lap siding, the Arlington boxes (linked to above) are pretty slick.