Body pros *I need some help*

I'm planing on molding my fender flares onto the fenders not sure what is the right material to use. I know i will need fiber glass and bondo or should i buy marglass? I'm also riding on air so i need somethign that will not crack on me thanks.

the flares have to be made of fiberglass for staters. then just rivet the the flares to the fenders as much as possible. then layed so fiberglass mating. i use to layers. the first is a small piece 2-2.5 inchs wide. the second is much large 6". make sure to get all of the air out. then let it dry sand the glass down then apply the filler. i would start with duraglass and then use filler over that.

i would use some bonding agent first "duramix or sumthingg along those lines then some dura glass