Fiberglass can be a real pain to get flat. Even the best glass can come out looking wavy if the prep work isnt done just right. The key to making it look its best is carefull prep work. Sanding is the key. use a guide coat spray, comes in a spray can but kinda spits paint leaving a speckled apperance. When the fender is block sanded the low spots still show the guide coat. Fill the low spots with a good primer and repeat the process. It can get tedious but take your time. When you get it right all the guide coat will sand off at the same time. A bare hand is the best judge. You should be able to feel it smooth with no bumps. Best of luck and be patient.
If you are refering to the body lines that are usualy the down fall to 99.9% of mass purduced glass there are differnt ways of doing it, assuming that you all you have to do is take material away, you can use a hand grinder with a stone wheel to shapen up edges and what not with it, keep in mind it will be messy and if you get a lot on you take a COLD shower, a hot shower will open up your pours and let it soak in. For edges such as the ones along the hood use a router good tool to use even to trim steel fenders.
Pretty much any type of abrasive tool will work and this is all assuming that you have a good eye for a straight line.
Well after a day and a half of glass work, bondo, much sanding, and several coats of primer, my front and rear fenders, and my hood are ready to be painted. I completely understand now why they call it a labor of love.
The truck is silver, so I am just going to do that. The cab is getting primed tonight. It wont be finish painted for ROR, but for the first time it is going to be one color, even if it is battle ship grey.
one word of caution, if your going to primer your truck, and paint it soon, thats cool, but if your going to leave it in primer, i would be careful, primer has to uv protection and will catch and hold dirt and oil from the road. then once its painted, you have fisheyes and other crud pop up out of nowhere.
I was going to get the truck finish painted this week, but ran out of time, and I am taking the truck up to ROR, so next week I am going to get it painted, that way it has plenty of time to dry. So after ROR it will probably be wash, sand, and finish prime.