4th time was not the charm, either. Last week we went on vacation. Before we left, I used an extra thick layer of sealant and specifically embedded the star washers and electrical lug in sealant and then covered the stack. I had such high hopes.
After we got back on Tuesday, I got some clear 3/8" hose to use as a manometer and hooked that up to the Left tank. I pressurized it to about 13 inH2O which is around 0.5 PSI. That was the pressure at which the balloon inflated. I left it overnight and was really disappointed the next morning as the balloon had deflated and the manometer showed only about 1 inH2O.
I haven't had the time nor the heart to try to find the leak yet. I'm really hoping it's from the filler cap, as that is considered acceptable by Van's. I really need to get the tanks sealed because I am essentially at a stand-still until they're done. Alternatively, I might buy another table and start working on the tail surfaces while debugging the tanks. Stay tuned.