Does anyone know of an internet resource for plans for a wooden camp bench, like the kind you see around the dining hall tables at summer camp?

I don't have a link for you but construction can be rather simple. Two 2"x8"x8,10,12' for the top two 2"x6"x needed height - 1.75" with the bottom inside corner clipped at a 45 angle, an apron made from 1"x4" pine and a few cross pieces made from 2"x4" or 2"x6" With those held on with carriage bolts.

Other than being sturdy, it is good to tip the seat slightly to the rear for both comfort and quick drainage. The back angle and distance between the seat and back are also very important for comfort. Three supports is probably adequate to keep the 8, 10 or 12 foot length from sagging. Speaking of sagging, if the angle is comfortable you should also avoid butt crack exposure in the gap between seat and back.