I have used RC56 a lot and it is a good glue for canopies for the reasons already mentioned. I have, however, found a glue that is much better. In its hobby guise it is marketed as PFM by Innovative Model Products. I have found that what PFM really is is an industrial adhesive known as E6000. Naturally, a tube of E6000 is much cheaper than the "repackaged" PFM. E6000 is already clear right out of the tube. Like R/C56 and silicone, when cured it remains flexible but is much harder/tougher. It's bond is also far stronger than either of the other 2. Likewise, it can be cleaned up with water before it cures.
I have found that large craft oriented stores carry E6000. In the St. Louis area there is a craft store chain called "Michaels" that has it as a regularly stocked item. I have also found E6000 at Home Depot. If you can't find it locally, you can get it here:
http://www.gluguru.com/Sealants.htm#e6100