If it makes you feel better just put insurance on it from DAN, it only costs less than $100 a year and covers floods. I did this when I started taking my video camera past the depth rating for the housing. The housing is rated to 150' and I have successfully had it down to 240'. But I don't think I'm going to be taking it much deeper, time for a new housing.
If you think about it I took it nearly 4 ATM deeper than rated, so for a housing rated to 200', well you might just make it to 300'.
Try at your own risk.