My experience may or may not apply here… In automotive paint refinishing back 15+ years ago, 2 part epoxy primers are special. Most primers are (were) 2k urethane. These are similar to automotive 2k clearcoat in how they work. They both have similar thicknesses, leveling after wet coats, and to a lesser extent - drying properties. With drying properties, the surface levels within a minute or so but it forms a surface film and the back side remains tacky for longer. (Where they differ is that clearcoat takes much longer to fully cure, like weeks to months, while primer is workable within an hour or less.) Epoxy primers are high build fillers. They get hard as a rock and are a pain in the ass to sand down. The two main reasons for using an epoxy are for super rough large surfaces, and this the the relevant bit here, they are used to seal the surface.

In paint, there are a ton of nightmare situations. Like let’s say some brake fluid got on the paint in a crash, or some idiot used rattle can enamel on a car. Often what happens is that the repair I am doing is not the first time the panel has been repaired. While I would like to clean the issue completely and use typical 2k primers, the previous repair may have used epoxy and buried something terrible. I’m not going to strip the whole panel and have to spray additional adjacent panels to color match when I did not estimate this in the cost quote. Epoxy seals out EVERYTHING. With stuff like spray can enamel, the painted surface never cures. It remains reactive to the solvent of anything sprayed on top of it. If ABS trim or bumper covers are exposed to acetone, similar issues with reactions will happen, unless 2 part epoxy primer is used. Epoxy primer is impermeable in the context of automotive paint; it is the nuclear option. Everything else allows some solvents to pass through it over time.

If you have ever touched the paint of new cars and noticed the softness, that is uncured clearcoat that is still venting solvents in small quantities. This is also why jams painting inside of the seals is kept to a minimum clearcoat thickness. The thicker the clear, the longer it will take to fully cure. As an ex pro painter, that softness tells me a lot about a finish too. It actually starts forming around 5 minutes after the clear is shot, just after the fingerprint test does not pull a string when removed. That is the first moment when I am able to barely graze the surface with fingertips and not damage the surface. It is still very wet underneath at this stage.

Hopefully that illustrates how even the hardest of painted surfaces is still able to allow stuff to pass through it. If you want to stop that stuff, you need a paint that is made specifically to seal everything.

That said, the seals and other materials also need to be up for the task. Most of those are likely just dust seals. How you deal with corners is critical. Just look at stuff like Pelican cases.

Not sure what type of humidifier that is but you may need a rotary one to get lower. There’s a technology connections video on them. They essentially are silica that’s constantly dis/recharging. They’re very energy inefficient but don’t have the same performance limits as compressor based systems.

I got one earmarked for exactly this before I moved. They’re simple enough I was planning gutting it and adding smarts using ESPHome. But moisture hasn’t been an issue for me so the project is a low priority.

Are you sure it’s 35% ? I’ve found those cheap digital hygrometers to be off by 10-15%.

I bought a box and some say 10 and some say 20. I ended up buying several different brands and price ranges of hygrometers to try and figure out which ones were correct.

I use cereal boxes with desiccant and without any active dehumidifier they stay at ~25% despite being frequently opened and closed. So like others suggested, put a large flow-through bin of desiccant in and forget about it.

I’ve done a similar thing using IKEA Samla Box (fits 6 rolls). With a few boxes of silica gel (dried periodically in my filament dryer) I can get it to stay relatively dry for a few weeks (goes from ~15 to ~25% in a few weeks).

I remember an article a few years ago about an experimental tube system that just rapidly dehydrated segments of filament in line on the way to the printer. Was hoping to see a commercial version of something like that by now as it just sounds so efficient. This setup looks extraordinarily unefficient on the other hand. I understand your efforts for better work flow, but to heat and dehumidify this properly will be a significant energy sink.

35% sounds amazing. I don’t know if you can get much lower

I am no expert, but in my own research for a previous task I had to deal with for work, most everything I saw said that getting below 30-35% for even a small room like a closet was going to be difficult without moving to heavy duty and expensive equipment. I don’t know if there have been improvements in the technology since then (dehumidifiers have definitely gotten much smaller) but you start getting into issues were you are pulling moisture from the surrounding walls and items in the room.
I suspect in you situation you May be able to make some gains with heat, but I have to wonder if how hot you can go before you start seeing problems with the cabinet itself. I have seen cabinet delaminate just from being in hot garages, so I am not sure how hot you can get.

Get some silica gel in there too

Wood breathes. You will need something watertight lining the inside. Paint is not enough. 8mm plastic is my first thought - but many plastics also allow moisture through and I’m not sure what is safe. An epoxy finish on the inside might work. But getting a continious layer could be a pain.

How well are those glass panes sealed to the wood? Could silicone the panes in. Doubt it would help you go lower, but I’m curious how much the dehumidifier runs after it gets to 35% to keep it there? I didnt realize they even made dehumidifiers that small, might have to look at them. 🙂