Re: Roughing It
If the essence of this topic is to actually increase degree of propolization of the nest (but not yet try another tweak at the carpentry), I say reconsider this entire thing.
I have plenty of propolization as it is without any tweaks.
Consider - touching top bars will cause bees to propolise entire "ceiling" of the nest. They really like to glue those top bars together so much so that the bars' wood is no longer touching.
Also consider - if top bars are not touching by design, cover them with a burlap (or something similar).
The burlap will be quickly propolised really, really heavily (again, creating a propolised ceiling).
Before bees will ever propolise any wall, they would rather propolise the ceiling first - because this is where the most energy escapes and bees want to control that.
So, what is it you really want?
Another carpentry tweak to play with (also fine if so) or to actually have more propolise in the nest?
Former "smoker boy". Classic, square 12 frame Dadants >> Long hive/Short frame/chemical-free experimentations.