OK, boys & girls, I checked the fit of the lid a few minutes ago. To test the fit of the lid all you do is put the lid on the humidor with the liner in place then lift it up briskly. If the fit is good you will feel a definite resistance due to suction. This resistance isn't due to parts drag because that feels different. And if the fit is good there will a very close, but not interference fit between the sides of the liner and the inside of the lid. It's not a good thing to get carried away sanding the inside of the lid beyond smoothing it and cleaning it up. The more wood you remove in this area the looser it fits. Seems logical, I reckon.
The next test is to hold the lid at the top of the liner then push down briskly. If there is a squishy, cushiony feeling when you push it down then you are good to go.
I'm happy to report that the project humidor passed both these checks with flying colours (for my Canadian friends
).