The flexure issues you read about usually refer to two long heavy tubes, eg a large newt for prime focus guided by an 80mm refractor and as Dopler pointed out, components like the arms of a newt spider flexing.
A few points to note :
Side by side (SBS) mounts are usually Losmandy D 75mm dovetails. I think the Star Adventurer is a Vixen narrow 50mm rail. Be careful or you'll order something very expensive that doesn't fit.
The dual SBS and other accessories are relatively heavy and will soon use up a large portion of your mounts limited payload capacity.
Note that most dual SBS setups cost hundreds of dollars.
I would think you should be able to mount the DSLR + lens on a solid tripod head or direct to the mount. The guidescope you mention has position adjustment rings to centre the guide star.
You could buy a short length piece of vixen dovetail V rail($40),
https://www.bintel.com.au/product/or...ounting-plate/
https://www.myastroshop.com.au/produ...sp?id=MAS-023L
make yourself a box cradle from 19mm pine. Polyurethane coat or paint to waterproof, and bolt a camera on one side and a dovetail finder base ($20) to accept the finder dovetail on the other. Make the box big enough to get your hand in there to loosen the locking screws. Yjis gives you dec adjustment in a lightweight setup, that's probably all that is required and a lot cheaper than a dual SBS.
Joe