Do your research
Before I created mine, I spent some time talking to the engineer at the Vans mothership, and here's what I learned regarding those access panels.
1) BLUF*, they did NOT recommend or endorse this sort of modification. They haven't conducted an engineering assessment on if/how the forward access panel mod strengthen or weakens the aircraft. That forward skin is structural.
2) Having said that, there is an engineering convention (don't ask me to ID the scripture, chapter, verse) that says basically if you're going to cut such a hole and install an inset panel:
a) it needs to sit on a doubler of the same or greater thickness of the surrounding skin material, and...
b) the area of the doubler needs to meet or exceed the area of the hole.
Take at look at the fuselage section of my Kitlog, starting on 1 Dec 2014. That'll show you how I went about applying this modification:
http://www.mykitlog.com/users/category.php?user=ScrollF4&project=879&category=6927
As you can see, I riveted the heck out of it, then used plenty of screws. I wanted it strong....period.
This mod has been an absolute moneymaker for work up front.
* BLUF = Bottom Line Up Front