The main idea here is preferably using customizablility than new parts like
-if your not satisfied with the length or size of the fuselage block than you can click the number and type the specific number your heart desires and if you use the buttons than it will add/subtract your number by 0.25 increments
-hollowness can be optional by size here's the instructions that would use this hollowness Add hole-->2->add/subtract 0.25 increments.
-Missile variants, you can increase the aiming reticle circle, lock time, range, speed, manuverability, but making one thing better makes another worse so OP missiles can't be created
And thanks for reading this