Hey there. I want to make a 57 chevy cake for my mother for her birthday coming up next month. I do not use fondant, so I want to use regular icing, but my concern is with doing the fins on the back. I don't care if I have to use some other type of food or candy to make this happen, I am open for any suggestion. I am usually creative, but a little stumped on this one. I am afraid if I try to carve it out of just cake, it won't hold. My cakes usually tend to be a little moist, so I know I am going to have to be careful on this one.

Can I ask why you don't use fondant? I just wonder because I was the same for years until I discovered MMF. I just think that you can really achieve your desired look with fondant. If your cakes tend to be moist, then I would suggest a durable 3D pound cake (in recipes section) It is great for carving! And carve it frozen (partially, at least). You tend to get more control.
For the fins, you could use RKT and cover in BC. Good luck!