Here are the tanks that Jon Johanson uses. They are tip tanks and add 12.5 gals each! So you will have about 3 more hours endurance with the extra 25 gal.
The nice thing about using the existing structure of the wing tip fairing is less weight. Weight of mod alone should be the same or less than SafeAir's 9 gal aluminum tanks. I like Safeair's design but have no first hand experience with either design, but the pictures look nice. Safeair may come up with more capacity since all they have to do is add a bigger "reservoir box" on the outboard end like the RV10 version they make.
Structural wise, I think the wing tip fairing tank would have some ties to the end-rib or spar web? 70 lbs of fuel on the wing tip held by the wing skin sheet metal may be OK, but I would like a "shear tie" between the tank and the spar or rib. I would ask if they did any "stress analysis"
Here is the link: