Big Strong Elastic Band brand recommended
Camera tripods use a standard 1/4" thread you can buy cheap nuts at Bunnings to fit and epoxy under a piece of wood to attach to tripod. On top of the wood screw in some screws so their heads are 5mm above the surface and space them a little wider than your dovetail and it will slide in and be held firm. use two screws for sides of dovetail and one as an end stop. dead easy to knock up.
Why not just use a camera? Seriously a camera is the same thing basically as a scope: an optical tube assembly coupled to a viewing mechanism. Got an old film camera with telephoto lens? then you just look through the viewfinder. No power needed or anything.