For all the guys who added the extention to their saddle bag.. doesnt it crack at the point where it joins to the bag?

It did with mine though I joined the extention with fiberglass!

Can the regular shaking of the bike cause such a thing?

how did you manage? any thougts?

 

My painter didnt use fiberglass.
Mine are bolted & glued on...then mudded in with body filler.