Glassing fins is *really* easy to do. Get some decent epoxy, a brush or roller, peel ply and some cloth.
Tape a piece of paper to your fin, tight over the fillets and body tube. Slit it and tape it down so the paper will sit flat. Trace the outline of both fins on the paper, then take the paper off.
Cut out the paper on the lines you drew then cut some cardboard templates out from that paper. Transfer any slits you made in the paper to get it to sit flat onto the cardboard too, so you can transfer it to the cloth.
Wash your fins and tube with acetone. Once it has evaporated you are ready to work. From the point you have used acetone onwards ensure you are wearing nitrile gloves (NOT latex. Latex is not suitable for use with chemicals).
You can then use the cardboard as a template for cutting your glass out. Draw a line in permanent marker (sharpie) offset by 1-2cm from the cardboard template so you have overhang. You should only need 1 layer for each fin pair, so you will need to cut out 3 pieces of cloth. The weave should run straight down the fuselage, and straight from tip to tip. Cut out peel ply another 1-2cm larger than your fibreglass. Always handle cloth to be used in composites with gloves on, your skin oils will create weak spots. You cannot clean your hands well enough to remove them, they are natural and part of you, and want to be on the cloth.
Mix up your epoxy, then you can either brush or roll some epoxy onto the fins/body tube (only do one fin pair at a time). Settle your cloth onto the fins/body tube, add more epoxy until it becomes completely transparent. Place the peel ply on, and then carefully work over it , making sure it's fully wet out (will go darker) and that there are NO bubbles trapped under it. The ply should be dead flat, and may have some pooled epoxy on its surface. If possible run a piece of flexible plastic like an old credit card over the surface, pushing down as you scrape. This will help remove excess epoxy from the layup and compact the layup. Again make sure you have no bubbles. Pay special attention to your fillet area - you want the glass to have no gaps here.
Alternative, you can wet the cloth out on baking paper (parchement paper) or cling wrap first, then move the wetted out cloth to the rocket, however this can make it much harder to get rid of bubbles later.
After an hour or two, when the epoxy is hard but still a little flexible (known as "green", its like a green tree branch.. hard yet flexible vs a dried branch, hard and brittle) you can tear the ply off and then trim the glass with a knife or scissors. When the epoxy is green, the epoxy and glass (carbon and kevlar too!) can be very easily trimmed. Move on to the next surface. If you want to speed up the epoxy cure, use a cheap fan heater or blow dryer. Keep in mind that when the epoxy goes on at first and gets hot, it will become less viscous and flow - this can cause your epoxy to slide off if you have it vertical... so ensure you only heat when the fins are horizontal.
Any twill or plain weave glass from 60-150gsm would do.