I agree - don't use a DSLR for long shots - not just the overheat factor, but audio issues. It's really not built for it. I use 'em for indie film, but those are short shots usually no more than 5 min at a pop and then camera sits and cools while we prep the next shot. Think seriously about getting something like an HMC-150 or even an old DVX-100. Your audio will go out of sync - unless you use the built-in audio which is dismal at best. Not to say it can't be done - I just wouldn't recommend it - I'd get something designed to shoot continuously for hours on end.
Jonathan Ziegler
http://www.electrictiger.com/
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