I reinforced the transom seperately,so I ended up using
5 courses all together on the transom.
I'm trying to remember, but after filling under the stringers,
I laid in a course in each panel (center, port, and stbd,
just in the bottom. Then I developed the radii on each side
of the stringers and laid in a 12" wide course in all the
stringer radii, followed by a course from the stringer top
to the stringer top in the center, and stringer tops to the chine
on each outboard side. Then finally a single course of heavy
roving in the center from stringer top to stringer.
I did this for the aft 7' of the hull. Were I to do it again,
I'd probably run it to the aft fuel tank bulkhead.
But keep in mind, my hull was suffering from cracking in
the area of the engine mounts.
If I were you, I'd just beef up the stringers w/root radii
and lay in a course, or two of about a foot wide in the bottom
and up the stringer sides.
Since you haven't ordered your tank yet, why not extend it aft
another 12"-15". It'd give you all the capacity you could ask for
w/o the complexity of a second tank. And please don't think
about widening your stringers to accommodate your plastic tank
as the stringers need to be on top of the inner lifting strakes.