Thoughts on best way to dry a micro build without a dedicated dehumidifier?

I stopped trusting passive drying methods after a Mobula 7 of mine started acting glitchy a week after what I thought was a harmless damp landing in wet grass. What worked for me since then is pulling the canopy and props right away, popping the flight controller board off the frame, and giving everything a quick blast with a can of compressed air to knock water out of the motor bells and connector sockets. Then it sits on a sunny windowsill for a day with the battery connector left alone untill I'm sure it's bone dry. Your filament box idea sounds reasonable to me, honestly. The one thing I'd check is that whatever heat source you've got nearby isn't warming the plastic canopy or the camera lens housing past what they'd normally see on a summer dashboard, because those little camera modules seem to be the first thing to complain. Warm is fine, hot to the touch is not. Also, once you think it's dry, plug in a battery and just let it idle on the bench before you fly. If the motors twitch unevenly or the board throws wierd errors, you'll know there's still moisture in a connector somewhere. A damp motor bearing is way cheaper to replace than a cooked board, so I've gotten in the habit of never rushing that first test flight after a wet one.

I never leaned into the idea of using heat for micro gear, and I think that's a critical difference. When I had my tiny quad, a 3-inch build with 1500mAh batteries, get soaked near a humid lake, I didn't use any enclosed warming. Putting heat near delicate circuit boards just felt like a huge gamble. What actually saved my flight controller was a two-day wait in a sealed Tupperware container crammed full of silica gel packets. I bought the large industrial grade ones from a hardware store, the ones used for camera lens storage. It wasn't a quick fix, but it was passive and safe. Since the components are so small, the moisture tends to soak into the plastic and wiring, and a low, steady enviornment is better than trying to rush the evaporation with heat.

If you are concerned about residual dampness, I whould rather let it sit for a full 48 hours in a place with minimal airflow, surrounded by high-grade desiccant, than risk thermal damage to the surface mount components. It really depends on how much time you have, but safety for the electronics is the priority.

The windowsill thing has worked for me too, I'll add that a silica gel pack in a ziplock with the board overnight speeds it up a lot. Had an Acrobee take a dunk in a puddle last winter, and after the air blast I tossed it in a bag with a couple of those desiccant packs from a shoe box and it was dry by morning. I also spun each motor by hand before powering up, any scratchy or gritty feeling meant water was still hiding under the bell. The filament box idea seems fine as long as you can barely feel warmth on the shell.

Had a Meteor take a swim in a muddy ditch last spring and the thing that actualy saved it was a bottle of 91% isopropyl from the pharmacy. Rinsed the board and motors in it after blowing the gunk out, and the alcohol just drags the water off everything and evaporates clean. Board was dry in like twenty minutes on a paper towel and it still flies today. Muddy water is the real killer, not the wet itself, so if yours was just humidity you're probably already fine.

The warm enclosure works fine, I've dried three wet builds in my filament dryer over the years and that thing holds around 45 degrees, gentler than a summer car interior. One thing I'd flag is the follow up a week or two later. Had a whoop that seemed totally fine after a damp landing in a swampy field, then a motor bearing seized up about ten flights in. Since then I put a single tiny drop of light oil in each bearing once I'm sure everything is dry, spin them by hand, and they keep running smooth long after the crash.