I'm not sure if this is where I'm supposed to answer you or not Steve ... but how could be offended if we hijack a thread that was inactive for 4 years? If this isn't proper etiquette, I apologize.
Short answer on leaks is my top is sealed up very well. Unfortunately, I am not as efficient and through as the rest of this expedition portal crew and do not have a build thread so show for it. However, I can say that I did my installation quite a bit differently than the one shown in this thread. Three major differences with my install compared to this one are a) I retained the front fixed portion of the Vanagon top (lots of modification required), b) fit the movable portion to the top to the fore-aft contour of the GM van (Vanagon's are flat), and finally c) added an additional seal across the forward edge of the movable top that contacts the original van roof.
Here's my reasons for each;
a) The fixed front portion of the Vanagon top does an excellent job of deflection the 70 mph wind up and over the top. This I believe reduces the opportunity for rain or air to be forced under the forward edge of the top under the seal (photo 1).
b) The standard uncut Vanagon top fits surprisingly well for-aft in it's uncut form, particularly if you push the top farther back on the top of the GM van (which is what it looks like was done in this thread). The reason I didn't like the mounting the top rearward is the opening in the roof also has to move backwards and you end up with the stand up opening too far behind the front seats to be as useful as I wanted it too be. Once you commit to moving the top forward, the flat bottom of the uncut Vanagon top cause the front of the top to ride up off the surface of the van ... making sealing it up near impossible. To fix this I scribed the contour of the GM van roof on the Vanagon top and got out my saber saw. Fits very nice and tight now (photo 2).
c) I did several tests with the wife driving up I-5 at 70mph and me running around with a mirror and flashlight to see where all the leaking wind noise/lack of contact was on the movable top seal. What I learned was the aerodynamic forces are signifiant on the front of the movable top and the outside front corners can actually lift enough to allow leakage under the parameter seal. To help this situation, I put a stiffener across the front of the movable top that not only stiffened the front but provided a location for an additional seal on the front bottom edge of the movable top (photo3).
Ok, way too much info ... probably could have stopped after the first sentence. I spend 25 years as an engineer working on door sealing of class 8 trucks and I know too much about what makes automotive environmental seals leak!
