To deal with runny epoxy, go to a local marine store, or Industrial plastics and paints to get a product known as "anti sag", "fumed silica" or "cabosil"..essentially glass fibers vapourized in a 3000 degree heat. Thickens epoxy and adds strength without a significant loss in flexibilty or gain in weight.
Add after mixing hardener. Can continue adding until you reach the consitency of peanut butter or use a small amount to slow the runs... cures clear in lower doses.
System 3 silvertip epoxy is nice to work with but lacks UV protection, yellows in no time. Their SB112 (formulated for surfboards) is a nice product with UV inhibitors, but prone to amine blush (greasy substance) if temperatures are not kept high.
Best epoxy I have used is a product called "resin research", cures crystal clear, UV stable and blush free, can blend slow and fast hardeners to achieve desired cure times and does well with thickening agents, tints and pigments, but only available in the States (fiberglass supply in Bingen Wash.), best of all most of the nasties are removed, so skin sensitization is minimal.
Have you considered 3m's 5200 polyuerethane marine adhesive for the task? Ultimate hold, good flexibility and absolute moisture resistance.
http://solutions.3m.com/wps/portal/...S4K7_nid=ZL0J5MTRJWgsQH8HT14PGTglVF59GPGLL3bl