The VAF Search is your friend
Al,
Do a titles-only search for 'access panel', and you'll see several good approaches to installing access panels on the forward skin. However, be cautioned: The forward skin is a very important structural part of the airplane's design.
When I called the Vans engineers asking how to go about this correctly, their immediate reply was "do not do it." At the time, I intended to make the entire forward skin removable by installing platenuts on the ribs, and to drill and tap #6/32 holes through the longerons. They
vehemently urged me not to do that, because they had NEVER run an engineering study of how such a mod might change the forward fuselage's structural strength.
Having said all that, one of the engineers told me that if I'm going to install access panels anyway, then please be sure to make the edge doubler AT LEAST the same area as the panel hole, preferably larger. Then use plenty of rivets to affix the doubler to the forward skin. Same for the screws that hold the panel to the doubler.
Click on my Kitlog link below, and browse the "Fuselage" section entries from Dec 2014. That set of entries gives the whole story of how I added access panels to each side.
You can see one of my panels in this photo:
As for how I made it watertight: I used non-paper gasket material from O'Reilly's Auto/Aviation Supply, trimmed to fit between the panel and the doubler. Each panel's 24 #8 screws has a #8 thin nylon washer. I have flown through IFR rain with this....zero leaks.
Note that I initially tried the Pro-Seal technique others have used. That didn't work for me, but you may have better luck. My gasket approach works fine.
Am I glad I did it? Most definitely, and Randy Richmond (my A&P) and Walt Aranow (my avionics miracle-worker) both expressed their gratitude as well. It made access to my forward electronics much easier.