I have a couple of the Chinese two-stroke angines, and they are buzzy little engines. You won't get away from the vibration too much. I'm afraid the plexiglass mount might ultimately fail due to the vibration.
The steel ones on my bikes have lasted for quite a while without problems. I broke the original cast ones right off the bat while tightening them. Dax has unbreakable steel mounts available: Page Title
To help dampen the vibration you may also want to take a piece of old innertube and wrap it around the frame where you clamp the mount.