Do hygroscopic filaments (PVA, Nylon) absorb moisture while in a heated enclosure
The concept that relative humidity decreases with an air temperature increase runs consistent with the concept of using a food dehydrator to purge moisture from filament spools. As the filament heats up, energy is imparted to the water molecules within. The dryer air around the spool will accept the moisture and &quot;distribute&quot; it to the environment. A warmed enclosed chamber will not have much humidity to endanger the filament.
I have a Sigma R16 and have moved the spools to the outside of the enclosure, but I don't plan to print hygroscopic materials in the near future. I suppose I'd have to build some form of drying enclosure around the spools, particularly for nylon and PVA.
My Qidi3D X-Max has both internal and external spool mounts and it is recommended to use the internal mount for nylon, as even an hour's exposure to humidity can deteriorate print quality.
PLA is safe for days, ABS is safe for perhaps less, but PVA is not a good overnight exposure material and nylon is definitely an inside-the-box condition.
I suspect that having the filament inside your Sigma, especially if you plan to fully enclose it, is not going to be problematic. I created a front panel for my Sigma to reduce ABS warping and the internal temperatures reached 37 °C. That's warm enough to keep the water clear of the filament, unless you have an extremely humid environment.
Before you add an additional heater, consider to place a perforated container of color-change desiccant inside the build chamber and observe over time the color change. Obviously when not printing, seal the desiccant from collecting non-test humidity, but I think you'll find it's pretty dry while you're printing.