I think the reason people generally recommend coffee bags are they are a lot less likely to contain chemicals since they are used for food. A lot of the chemicals listed there are used for treating bugs on tree's and should not be found in coffee bags.https://www.gardenguides.com/about-5030516-chemicals-burlap.html
Not trying to say it's bad I used burlap from coffee sacks as smoker fuel for years with no problems. Just something to be aware of.
This would help with insulation, but it probably will not help as much with moisture since there is not much area for moist air to mix with the wood shavings.I am thinking of using my top feeders that hols about 2 gallons of sugar water. Instead of water fill with wood shavings. Bees could get in but doesn't seem like an issue.
I put a 1x2 (ish) board down the middle of the box about 1/4" up to support the wire mesh that I installed. With it stapled on both sides of the box and on to the cross bar in the middle it seems to stay put well and not sag. Since there are still 3+ inches of shavings above the bar it maintains the insulation properties.interesting about the chemicals in burlap.. can't anything be safe these days?
So- I found a roll of fiberglass window screen (basically plastic screening) that I figure would work fine/ guessing it's inert. I'll just stretch across box/staple and then put it on top of queen excluder (to prevent sagging into candy box).