I've done several fiberglass bows and used Bingham's glass on every one of them. Once I began to make self bows I stopped making glass bows because all-wood is more fun and has very few of the annoying traits that glass has for the woodworker. Those would be glass slivers, epoxy allergies, glass' propensity for dulling tools, the need to run a bow oven, respirators when sanding, etc. If you like working with wood you will find glass frustrating. Working on a glass bow is more like machining than woodworking. Having said all that, glass would probably strengthen your bow's belly. If I were going to do that I'd put the glass on the bow back as well and glue the whole mess up at once. Sinew is a bit of work, I would never do that and have glass on the same bow...but to each his own. You'd be wise to order more glass than you think you need. I never nailed the draw weight on the first attempt with a new design. You'll likely do the job at least twice to get what you want.
I do have to ask the question - since we're on a primitive bow forum; if you need to strengthen a bow's belly for your primitive bow application, why would you not do one of the 2 solutions that are primitive? 1 - choose a limb wood that is better in compression, ie osage or ipe? 2 - do the primitive belly strengthening approach...horn? I have a 2"x3"x40" squared board of relatively green osage I'll send you for the cost of the shipping if you'd like to use a better bow wood in your application. You'll need a good table saw and/or band saw (and some persistence) to rip boards like you want. My band saw absolutely refuses to rip straight osage boards. I cannot help you with horn.
Good luck,
George
