I would endorse the idea of sealing/coating, but more for appearance than anything else.
Moisture absorption ... with pine and MDF maybe. Rather doubtful on well-aged hardwood though.
Resonance? Mine does NOT resonate, that's for sure. If you build it out of 2x2" pine it might though. The sticks would have a much higher slenderness ratio.

I did try anchoring a machine (actually a robot) down once with concrete paving slabs. It walked. The hydraulic actuator on the main arm hit resonance...

Cheers
Roger