For parts like what you're wanting to make I think the fastest and easiest way would be to make fiberglass molds. You're going to be making the parts out of fiberglass so you'll already have the materials and the skill to use the glass with no learning curve. Split the part in half, mount to a flat board then body work, prime and sand down to 600 grit just like the way you prep fiberglass for paint. I like to use 3/4 ounce cloth for the first layer (for mold and finished part) for anything where final surface finish is important so you get the smoothest possible part. Next add a few layers of either 6 or 9 ounce cloth. If it's a bigger mold that needs to be really stiff I use a layer or two of the heavy cloth or mat like what you can get at the auto parts stores or Wal Mart. If you cut it into smaller strips it will conform to pretty small parts. Every time you mold something, whether making the original mold or the final parts you need to use some type of mold release, I use PVA (polyvinyl alcohol). You can brush it on with a foam brush or spray with an airbrush and it can be found or Amazon or at O'reilly. In addition to the PVA I like to wax everything (either mold or plug depending on what stage you're at) really good before applying the mold release. Some people will tell you that you only need one or the other, but I like to use both as extra insurance. Plain old Johnson's paste wax in the yellow can works as good as any of the specialty mold waxes for this.