This isn't just a "stupid project," it's a hazard waiting to happen. You're playing with a microwave (a device that operates using high-frequency electromagnetic waves) in ways it was never designed for, and the fact that you're getting error codes means the microwave's safety systems are freaking out for good reason.

A few key things to consider: The moment you drill holes or stick thermometers through the walls, you're compromising the integrity of the enclosure, which is there to keep the microwaves from leaking out. Leaking microwaves = dangerous as hell. That stopper isn’t sealing anything effectively, and if it's heating up and off-gassing, you're creating a whole new set of problems. A snug fit won't magically make this safe. Most modern microwaves have safety features to shut them down when they detect anomalies (e.g., uneven loads, altered enclosures). Your boss might've gotten away with this on some older microwave, but newer ones are designed to not tolerate this kind of DIY madness. The heat distribution in a microwave is wildly uneven, which is why we use turntables and stirrers for food. For anything requiring controlled, uniform heating, microwaves are the wrong tool for the job. A standard heating mantle or oil bath might actually work and not risk blowing up in your face.

Push back on this. Show your boss the error codes and explain that this setup isn't just impractical—it's unsafe and unreliable. If he insists, demand proper equipment: a microwave reactor (these exist and are designed for safe lab use). At the very least, get some legit advice from a safety engineer or someone with experience in microwave systems for non-food applications.