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Let's back up.

What are the known problems with the hull other than the old gelcoat?
Posting photos helps us help you.
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If you think the hull has significant water intrusion, you need to get the bare hull weighed. The only way to really know is this step.

There are NO STRINGERS in any Boston Whaler hull.

The foam is a structural element of the hull and if you cut it out you need to re-bond new foam or add stringers.

If removing the foam is appealing, and you want a flat floor ,you don't really want the features of a Boston Whaler and should just sell what you have and buy something else.