Working with epoxy mud is just plain messy, messy, messy. First thing is to mask the area. For a glassed structural joint there are guidelines for fillet thickness and width. If you just keep in mind that the chine should be at least as rounded on the inside as outside or something to that effect. In other words two 4mm panels meeting at a 110degree angle don't need a 2" wide fillet that is 8mm thick. 5+mm thick and about 5/8" wide is sufficient. This is a totally unscientific and experiential number. Make your goop, toss it into a zip lock freezer bag (not the freezer), cut a corner 1/4" then squeeze it out in a line. Come back with tool and smooth goop, pull up tape. Let 'poxy cure part way then come back with a littl dish of alcohol. You'll be amazed at how glass like you can make the fillet. Wearing two pairs of latex gloves will help as you dip fingers into the alcohol and smooth the partially hardened epoxy.