Just finished building the new floors and casting decks in my boat and I spent some time thinking of this problem...how much access do I need to the new underfloor fuel tank.
I was thinking of cutting the main floor into 3 pieces, 1 piece that covered just the tank for easy access.
In the end, I went with the 2 piece floor, split down the middle. Still easy to remove, but don't want to do it every week
As for your stainless screws binding, I put all of my screws in with Silver Goop. It's a product we use at work for fitting stainless machine parts together that we want to come apart some day. I've been using it for about a year in the boat, and undoing screws no worries..