Questions about painting and internal decals

[plinth]

Hey all, shell painting noob here approaching my first paint job with a wary kind of anticipation!

I have a Supastox that I want to fit with the Porsche shell. I'd like to give it the Martini colour scheme. Would this be best achieved with a decal set, or masking the stripes individually?

Also, does anyone make decals that are fitted internally to a shell before painting? I imagine they'd look much better than ones stuck on the outside.

In an ideal world, I'd stick a bunch of Martini decals on the inside of my shell, then give it a few coats of white and we're good to go! I appreciate however, this could be a very naive viewpoint!