I have not done this either.
My thinking is the portable gaso tank currently goes in the open area by the transom. You want to create a gaso tank locker in the enclosed area that currently has foam in order to clear up some space. If that is correct, I might consider leaving the portable gaso tank where it is and instead create the additional storage in the enclosed area that currently has foam. However, you will need to figure out how you would replace the lost flotation.
Of course, my assumptions may be incorrect, in which case I'll say "oops".