I also have the same setup and fortunately have never had a flood. Are more expensive housings less likely to flood? I have not seen a head to head comparison of housings flood potential. Maybe the insurance companies have enough aggregate data from flood victims to help us find the housing least likely to flood.
I have the same set up, a 5D with an Ikelite housing. I would be very interested in knowing what caused the flood? I have flooded mine once, but that was my own fault.