The bad fuel tank isn’t too bad IF you like to do DIY. However depending oh how wet the stringer is, it could be a really big deal. I am going to replace one of my fuel tanks this winter. I love working on my boat, but stringers are not on my list of things I want to do. BTW, welcome aboard.
If you are one there is no explanation necessary.
If you aren’t one, there is no explanation possible.