I'm confused, maybe!

I'd probably use 3-1/4" (6mm) bolts (or 5 smaller) with small washers to hold the fenders on. Using a limited number of small bolts and small washers might allow the fenders to be ripped off (given an unfortunate experience) rather than doing a lot of damage to the tear. I think clear silicone would be good to seal the fillet between the tear and fender. A technique that works for me when "siliconing" is to mask off on either side of where you want to put the silicone, silicone, use something to form the fillet between the masking tape, and then pull off the masking tape while the silicone is still "wet". This leave a nice "fillet" with clean sharp edges. If I haven't answered all your questions let me know. Hope I've helped.Cheers,Gus