Ives tried to use resin to fill prints and it ended up leaking all over and making a mess. I’m sure with the right geometry and enough perimeters it can be done, but keeping the walls sealed is an important consideration.

My preferred approach to weighting models is to design in holes for bearing balls and press them in, with optional (and lightly applied) adhesive.

I do have a circulation fan but I only turn it on for materials that want more cooling like PLA. For higher temp materials (mainly PETG but I also print some ASA, PA, PC, TPU) I keep it off. Which is a little frustrating because I got it originally to circulate air through a carbon filter for fumes from those nastier materials.

My mk4s is in an official prusa enclosure and I still get warp on large parts. Depending on the part I will take one or more of these additional measures, they all help:

• apply glue to the build sheet
• add brim (I resisted this for a long time but I gave in and it’s easily the most effective thing for parts with large flat bottoms that I can’t redesign)
• reduce perimeters and infill%
• redesign the part to reduce bending stiffness
• preheat for 30-60 minutes

Cnc is fundamentally different from 3d printing in that the tool head and workpiece apply significant forces to each other. You need rigidity to deal with that and belts don’t provide it.

My dryer only goes to 65 but that’s what I dry my overture petg spools at and I haven’t had any issues