I found a set of 3 round boxes at Safeway (Northern Virginia) on sale
with Safeway card for $1.99 for the set. They are heavy duty plastic,
air and water tight, safe for freezer, dishwasher and microwave (that
covers hot, cold and wet). The largest would make a slightly small
letterbox - but it can easily hold a 3"x3" log book along with stamp,
etc. I figure the smaller sizes could be used for miniboxes. The
smallest could even be used to hold a stamp within a larger box.

The set consists of the following round boxes (measurements are
interior):

(1) 4.5" across, 2.1" deep

(1) 3.5" across, 1.75" deep

(1) 2.5" across, 1.25 deep

There were several other sets with different size containers. One set
did have a couple rectagular boxes that would work as well, but the
rest of the set was too large.

The closing mechanism is different than Tupperware or Rubbermaid.
There are four hinged tabs on the lid that click over protrusions on
the edge of the box. The brand is Lock & Lock and you can see them
online at the following site, but they are much more expensive here:

http://store.heritagemint.com/escalate/store/CategoryPage?
pls=heritagemint&bc=heritagemint&cc=LL&group=cat_prod&clist=0137803261
f9&startNum=12&rangeNum=6

(this is a longggg URL - you might have to cut and paste in sections
into your browser)

I have boxes, carving material (Enough for at least 100 stamps! I
have to try all the types right?), 6 stamps carved, plans for 3
series, I've planned the parks where I want to place them. Now all I
need to do is make some log books, and get out and plant the boxes!!
My goal is to get one out sometime before Christmas. :)

--Mahjong