Don't tell your local composite supplier, but after a successful vac bag process, if you quickly pull the top sheet away from the mastic seam, you can re apply the waxed paper tape and with a little care, you can reuse the bag again and again.  Key to being able to do this is to lay additional layers of "used" bag or sheet plastic on top and bottom of your work so that the epoxy never really comes in contact with the outer bag........saves a little time and a little landfill space.

use of unidirectional glass

ready to roll. ( epoxy that is) ...........the vertical stiffeners that are bonded to the hulls and the outboard sides of the centerboard cases include a modest amount of unidirectional glass along the edges. 

centerboard support webs

Here are the six support webs that will make up the structure that will transfer the loads from the  centerboard cases to the internal sides of the boat.  I have found it easier to first cut and lightly bond the glass over the foam using 3M-77 spray adhesive then simply roll on a good thickness of epoxy over each piece and vac bag them in the usual manner.  After performing hundreds of vac bag proceedures, it's possible to get a feel for how much resin each piecs will absorb.  If you over apply, it won't hurt your part, it will just hurt your wallet.