Look at the Selig 3021, and a 8-10:1 aspect ratio.
No ailerons, for a clean wing surface.
Dihedral/ployhedral for stability.
A 4-stroke is much more fuel efficient than a 2-stroke.
With 90 oz of fuel, you should get much more than 100 miles!
The California Marathon planes on 64 oz. fly for 8 hours plus, 300 miles plus!