Oil tank placement between stringers

[SailorChlud]

Good Morning: I am thinking of digging out the foam between the stringers in my 1972 Seafari in the rear starboard locker so that I can mount the oil tank lower. In essence, cutting an 7.5 inch by 10 inch rectangle of foam out. As of now my tank sits on top, but it takes up a lot of room in the locker so that taking the battery in and out is a pain, and water puddles on the top of the foam area.

I was thinking about turning the oil tank 90 degrees, so that the width is about 7.5 inches, and was hoping it would fit between the sides of the stringers, riding lower so I had more clearance above it.

Here are a couple of photos showing the current placement.

Has anyone dug out the foam between the stringers? If so, could you measure the clearance between them? I don't want to cut it out only to find the opening is too narrow. Thanks for the help.