lol -- gas caps are a major culprit in leaks for sure.
Small leaks can be really hard to find though. Unless you happen to bird dog it somehow, you may need a "smoke test" where chemical smoke is pressurized into the system through the filler neck and you look for where the smoke is coming out.
This requires you to force the vent valve on the cannister shut because it's a normally open valve. The vacuum control valve in the engine compartment is normally closed so you can simply unplug that.
I currently have a small leak with is a problem this way: my EVAP diagnostic monitor won't complete, but the leak is so small it doesn't light the CEL. Very strange. I've done some testing with forcing vacuum on the tank and then forcing both valves closed (just using jumpers) and I still haven't been able to find it.
It's sometimes a problem even for regular service folks to diagnose. I hear lots of stories of people throwing parts at it to fix it which seldom works.