It is impossible to hide a ship, ANY SHIP, inside a planet or star.
The atmospheric and coronal deathzones are not hollow. They extend from the center of the sun or planet all the way out to wherever the edge of the atmosphere or corona is.
No matter how much hull the ship has, eventually it will die from the constant hull damage.
Besides, why would someone go through the trouble of making a completely new ship simply to save a slot when they could just undock with the character they're trying to save a slot for (Because you'd have to be able to log on in order to get on the camera ship character, so why not just log onto the normal one?), cruise up or down from the plane a good 50k or so, and then do a full stop.
I do similar on my morph when I'm trying to do some roleplaying without the risk of being mobbed by twenty people shouting "OMG MONAD DAI!"(An exaggeration, usually it's two or three, with a couple others that are actually willing to RP with me.
Characters Alan Markson: The Hellfire Legion's Lord Commander The Perihelion: Freeport Four's guardian, and yet much more. Missing and assumed Lost with all hands. Eric Dresmund: Junker, smuggler, thief. Last seen drunk on Beaumont Vayrn Wyard: IMG Recon pilot turned Neo-Terran Captain. Last location unknown