crazy ? about culverts

[strmchzr]

guys,

i need some "experts" opinions concerning placing a 5' long (48" D) metal culvert on end to create a one man pit blind for duck hunting in a shallow marsh.

http://img328.imageshack.us/img328/3...pipepit0em.jpg

how can i "cap" one end of the culvert and make it watertight?

any ideas how i can anchor 4~5 of these "pits" so they don't float when my marsh floods?


i really appreciate any thoughts, ideas, etc. that ya'll have concerning this project!