40 thou styrene sheet would be fine for that size nose bowl. Styrene is weak. Since you have the plug for the pull go ahead and 'slick' it up. Paint and wax it. Attach to a parting board. Apply mold release. When dry start adding glass and resin (I like polyester) to make a mold. Repeat the wax and 'release' with the mold and lay up your nose bowl. Sounds complicated but isn't. The part will be stronger than styrene, you need the nose weight and all your friends will wanna build one now they know where they can purchase one of the more difficult (in their minds... hehehe) parts!