I've used RC56 and had horrible results...just wouldn't stick, so I switched to silicone...which worked better but I couldn't make it look 'clean'. Recently on RCU there was a post about using a product called Fletch-Tite. This stuff is used for fletching arrows and can be found in archery stores for about three bucks. Simply fit the canopy to the fuselage and tape in place every 1" or so. Apply a tiny (the smaller the better) bead of the Fletch-Tite to the edge where the canopy is contacting the fuselage. Let dry for an hour or so. Remove the tape and apply the glue to the remaining areas. Let dry for an hour or so. You can optionally run another bead along the entire edge.

The canopy will be sealed around it's entire perimeter and won't come off without a large amount of force. The glue around the edge will be barely detectable...the Fletch-Tite shrinks as it dries. This stuff is great...for $3 you have to try it!

-Tom