Well if you can, get the WestSystems fillers. It seems to be the cheapest around here. Ask for 410 microfibers. It should be a Tan coloured powder. Easy to mix and work with and cheap
. DON'T go for the dark brown Microballoons. That stuff is expensive and harder to work with. I find a hand full of the white silica powder 406 thrown into the mix allows a "mayonase" mix to not slump. However, a very thick "peanut butter" consistancy is what you will be needing, so you probably don't need the 406 at all. Mix the 410 As thick as you can make it as this makes sanding
easier. You will most likely need a 20ltr bag of the stuff.
I also suggest you go for a summer grade hardener. Once again, if it is west system, then you want the 105 Resin and a 205Hardener. Careful as you have a pot life of about 10min and in any bulk quantity, it will heatup and go of in a minute. DO NOT use the summer hardener if you are filling any area over say 25mm deep. It will get too hot. The 206will be hard enough to sand in about 6hrs. The winter hardener will give you a much longer work time and allow you to fill much larger volumes, but will start its curing process in about 45min and will take about 12hrs before you can sand.
For shaping, obviuosly, the closer you can get to the finished article, the less sanding
after cure. So cut some shapes from plastic of what you want as a finished fillet. USE GLOVES, it is a messy job no matter how careful you are.
Hope this helps.