As best I can tell and I am often wrong, to make room for the added living space and still keep fuel capacity they tried to get fancy and contour the tanks to the hull.
On the other hand, the lower (cheaper) Sedan has mostly box shaped tanks that are accessible on all sides.
PO had them coated by hand, inside and out. Seems to be working [emoji106]
If and when they fail I will go with three 50 gallon spun polyester tanks on each side, plumbed in series.
It's been used and still on French helicopters since '78. No problems, except when you crash hard. Then they burn[emoji30]