Well, I bought a length of guttering, put the end caps on, filled the
gaps at the end with gutter seal, and it holds the water just fine. It
also looks like it will do fine for boxes up to about a #8, 4 feet in
length and 5-6" in width.
I tried heating the water over a dual hot plate, and after about an
hour, the water was still only at about 150 degrees.
Any ideas on the best way to get the water to boil?