You should glass the inside for strength, HOWEVER, in my experience, epoxy resin doesn't adhere well to the ABS. What I do is rough up the inside of the cowl with some 220 paper, then I position A SINGLE STRIP of fiberglass cloth inside the cowl and use THIN CA to adhere it. Once that strip has dried, I repeat the procedure for the other strips (I usually use strips about 8" x 1 1/2" ). You need to get the strips smooth against the ABS before applying the CA, otherwise the CA is going to set too fast to press the strip against the ABS (getting the glass strip smooth can be a pain with wheel pants ).

I suggest doing this IN A WELL VENTILATED AREA .