3) THE WATERPROOF CONTAINER:

The basic requirement is that it be waterproof and hold the stamp and notebook comfortably.

While others have researched a cylindrical tube from a surplus supplier, I prefer Rubbermade containers, of which two seem to work. My favorite is a #3865 "Servin Saver - size 11", measuring 4"x7"x2" inside, nice smooth white cover for a label.

They also make a similar size, #5534 (size A), blue cover, more rounded sides (shown in the earlier photo). This size will allow the notebook (and some postcards) to lay flat inside. 

Which ever you can find (try Wal-Mart or anyplace that sells housewares) works OK; I like the white one when I can find it. Either way, squeeze it to make sure the seal is good - one that I bought wasn't. Cost $1.50 - $2.00.

Make a label for the cover, again, with the Letterbox name, and where to contact you if it has been disrupted. And, a PLEA for the finder to respect its contents. Keep in mind, unlike Dartmoor, the odds are high that a chance finder won't know a thing about letterboxing.  Mine say:

"XYZ LETTERBOX. PLEASE DO NOT DESTROY. Enjoy the contents, and replace where found, hidden from view. To Learn More About Letterboxing, Visit the Letterboxing Web Site. If Contents are Damaged Or Missing, Please Call (my name and telephone number)"

I stick this onto the cover, and cover tightly with clear tape that I hope will remain water-resistant for a while (we are still searching for the ideal waterproof tape).