Car repair putty is porous and will eventually bulge and fall off like a leech and epoxy is the best of all for fixing fibreglass.
The concealed gutters are fixed just before the eaves. RoofGard-SB is a great high quality underlayment and is completely waterproof. https://Beeinmotionri.org/an-over-see-of-rubber-epdm-and-epdm-flat-roofs/