Here a tip on using Epoxy Resin like you would use a caulking gun to fill cracks, seal joints, and even 45 and entire joint with fiberglass.
1. Catalyst to Resin Ratio.... For best results use approx. 1-1.5% max 2%
1 cup of resin to 2.4 - 4.7cc
1 Quart of resin to 8.5 - 19cc
2. Mix Cabosil in resin only before you add catalyst
Micro bubble powder (Cabosil)
For 3 cups resim use 1/3 to 2/3 8oz cup Cabosil
For 6 cups resin use 2/3 to 1.5 8oz cup Cabosil
for 10 cups or 2.5 Qts. resin to 1 coffee can Cabosil
Do not mix in front of a fan. Cabosil is easily airborn. Mix with a drill and paint mixer. Only catalyze as much as you are ready to use. The rest will stay good for a few days if covered.
Mix paste to desired consistancy. You can also add a surfacing agent that will allow you to sand the finished product.

I went down to the corner Bakery and paid $1.50 for a dozen cake decorating funnels. Also at Restaurant supply you can buy these plastic cake decorating funnels 100 per box. They work great with Mico Bubble Resin. The end may be cut to the desired size you wish to caulk. Use a plastic putty knife cut to the desired size. As you pull the excess from the joint. save product and reuse back in the cake decorating funnel.

This is one of my Epoxy Resin Paste reinforcement joint: