I liked that idea too. I think you could fiberglass a wall (with drains at floor level) between the benches then get a used lazarette lid and cut it down for the top. Of course I'm painting my whole boat so I could do this and make it look factory.
That'd be slick. Ideally watertight, but that might be asking for a lot.
The concept in general is a great one, with lots of ways to go about it. I know some people never experience issues with the factory arrangement, but in my '79 I was constantly plagued with fuel leakage issues, even with a brand new tank and lines. It drove me nutz.
Anyway, kudos to Mike for his fuel locker, and a big thanks to Stingy Sailor for all he has done to promote this stuff.