If you are going to use locust, bear in mind it's fantastic ability to split. Clear wood will do this more than #2 with knots. Be sure to drill all holes and support with crossmembers real well so that it doesn't split up when you go over a lot of bumps. It does give a nice yellow/orange look when finished. If you really want a tough bed - use hedge (osage orange). It won't rot either.
