I don't own the Star Adventurer so I can't comment on its stability. I have used an ED80 on a small mounting of my own construction and can make some general remarks that will apply to your situation.
If you hang a camera or a 2" diagonal and say a 26-40mm 2" eyepiece, that will add about 1 - 1.5 kg to the payload. I use an Andrews 30mm UWA (80 deg) eyepiece with an ED80. Fantastic sharp wide field view 4 degrees with a 4mm exit pupil. Good for old eyes! But it does add most of 1kg to the back end. You may even need to hang a counterweight band around the lens hood if the balance point gets shifted backwards past the end of the dovetail.
For a given weight of OTA, a short OTA like a Maksutov will sit more steadily than a long refractor of equal weight. The longer tube applies more torque and will oscillate more.
The illustrations of this mount frequently show the OTA well away from the polar axis and counterweight extended toward the end of the thin counterweight shaft. This will cause it to oscillate like a pendulum.
http://gerrygibbscamerawarehouse.com.au/images/en_mounts_caty01398815932.jpg
This can be minimized by pushing the dovetail so that the OTA is as close to the polar axis as possible, not hanging out like they show in all the illustrations. Bolt a counterweight to the 1/4" tripod screw at the other end of the dovetail _ a camera with lens if nothing else so that the counterweight on the shaft can be moved as close to the polar as possible. This will minimize bouncing.
Joe
