About to fit and install the back window. Plans say to tap both the window and the rollover structure for the attachment screws. As paranoid as I am to avoiding any sharp edges on plexigalss canopy/window, I am perplexed as to why I should tap both the plexiglass and the underlying structure. Seems to me that I will introduce a helix of sharp edges at each screw hole by doing so...and what purpose does it serve versus a smooth hole? How did this go for those that have done this?