For what it is worth, I installed a plastic tank from a 96 Caprice in my 69 Camaro - with some mods.
It has a factory vent line that I attached to a charcol can set up from a late model GM 1500 pick up. Since the car is fuel injected with the LS and return line...the LS computer also had the output and my Painless Harness had the purge line connections. No brainer - hooked them up and put a sealed cap.
Long story short - no odor, no leaks, no issues - it acts totally OEM.
I also did a 69 Corvette a few years ago with a stock 69 tank - I used an early 90s full size Chevy truck charcol can and mounted it next to the tank. I ran the vent to it - and no vacuum from the engine. I ran a sealed cap and had no odor or drip issues.
I know that is a bit off topic, but I do think if you have a larger vent line - then run it through a OEM charcol and in the best case hook to the PCM through the valve....your drips and odors will be gone.
I'm not saying the caprice mod is easy - but it was very inexpensive and allowed use of multiple OEM parts including OEM quick fit lines...etc and proper vent tubing.