Dometic 320 Installation Video.....
LINKThe old toilet wobbling is probably due to toilet to floor flange bolts being loose, floor flange installed too high (bottom of flange should rest on floor) or floor flange not secured to floor.
You won't know about the floor flange until you remove old toilet.
You can check the toilet bolt tightness on old toilet.
While you have the old toilet out....might want to install toilet water shutoff valve. Nice to be able to isolate toilet water without having to turn ALL water off.
The 320 Is a nice upgrade from that 210. Good luck!