I got a 60qt Ziploc WeatherShield and the gasket in the lid was too thin so the latches would barely latch and not tight. So I got this from Amazon and it worked great.

https://www.amazon.com/gp/product/B07477J8KL 

Fit like a glove and it seals great now. I installed on top of original gasket.

FYI for any who have a similar issue.

in use pic
http://warriorbreaks.com/misc/tupperdor1.jpg 

Despite the angst often experienced in getting wood humidors to seal reliably.....I find that my coolerdors, sterliteadors and rubbermaidadors work best when the seal is sucky

Work best how?

Mine was not holding humidity well but this fixed the issue.

Because you don't want the seal to be perfect... or at least that's been the common advice. Want a little bit of air exchange (I'm guessing to avoid issues like condensation or anything else that may cause standing water).

I've never used a non-wood humidor, but when I was interested in it years ago many of the instructions included ensuring it didn't seal completely... either by choosing a cooler that didn't seal like tupperware, or I think some advised a small hole.

Of course, I'm sure that with something like this, your local climate probably plays a big factor.
If you're in a location which is very dry, a full seal may actually work better....

If you're in a location with very wide temperature swings, then condensation inside the tupperdor may become a higher risk.