Since you're using a lace frontal you need a good base that's structured to add it to.
Instead of the stretch cap I would use an actual weaving cap that looks like what you'd get in a BSS wig (2nd image image, @ BSS) *sew the frontal on here, then cut away the extra netting from the cap*
Or get a glueless lace wig cap, that you can replace the lace in the front with your frontal (1st image, you can get these off ebay) *Sew the frontal on, don't glue it, otherwise you probably will not be able to use it again*
Good luck, I'm not ambitious enough to attempt this!
Edited by godgavemecurls - Feb 06 2014 at 2:41pm