I have installed quite a few canopies on RVs over the years. At least a dozen or more. So far none have cracked.
I have never used sikaflex but have always drilled the canopy and either used rivets or screws to fasten them.
When using screws, for example on the RV8, I initially drill the canopy to the frame and cleco it on. There are some high stress areas, noteably behind the cross brace where the tubing size changes. I typically do not put anything in that area, for maybe 8 inches or so, depending on how the canopy is fitting, but leave it to float. The canopy does require some pressure to make it conform but I try to reduce that as much as possible. The way the canopy rests on the frame is critical. It is important to initially get it to rest as snugly as possible all around the frame before you drill any holes. Once you drill the first hole you are committed.
I drill the frame holes to #35 and tap threads into the frame for #6 screws. Just chuck a tap into a drill and use some Boelube. Debur them before putting the canopy back on.
Then I drill out the canopy holes to 1/4" using a plexiglass drill bit. If any of the holes look rough, I use a pencil soldering iron to touch the inside edges of the hole and seal any tiny cracks or burrs. Usually, I just do them all, just in case.
The countersinking for the screw gets done on the skirt.
Also, sand and smooth all the edges of the canopy.
When installing the canopy, I use the vinyl hose washer Paul mentioned on a few of the holes, just to line things up. The rest I leave open for maximum expansion and contraction.
If I am riveting the canopy on, I drill to at least 3/16" on the canopy and only use a hand blind rivet puller, since the pneumatic pullers can pull with too much sudden pressure, in my opinion. I always prefer a 1/4" hole in the plexiglass but if the skirt is trimmed a little close, the 1/4" hole may show a little, so I go to 3/16" and so far it hasn't been an issue.
In spots where there is a space between the canopy and the frame, or the skirt and the frame, use nylon washers as standoffs to keep the pressure off the canopy/skirt. You may have to stack them in some places to get the fit just right. It will make everything look nicer and relieve stress areas.
Fitting the canopy can be stressful.
Hope this helps and good luck.