Mitchell Gass concluded:- This would mean that any water that gets in the seat tube would collect abo ve the bottom bracket shell and have no place to go, and I can imagine seri ous problems with rust at the bottom of the tube even if there are no signs of rust higher up.
In all my years of riding and maintaining bicycles have never found this problem that can be overcome by checking the bottom bracket regularly. This ofcourse depends on the type of use and weather the bike has been used. For example a tourist rider with mudguards/fenders and mudflaps would need less attention than the racing person with a stripped down machine. Both water and moisture internal problems are a fact of life when it comes to owning a bike and regular attention to the "weak" areas is paramount.
I would suggest to Mitchell cast aside any doubts of a frame construction that has being manufactured in their thousands without any problems that ca'nt be overcome providing they are look after treated with care and