Hi Exp,
I am a quite new user here, and probably this is why I can't add post to your question on legal matters regarding designing a papermodel based on a copyrighted artistwork.
I can help you with this issue, while you can help me to let me know how to become a full-right member, for example capable of posting :smile

)
back to your issue:
All works of art - movies, drawings, plans, papermodel desiggns, etc. - automatically enjoy copyright protection from the very moment of the generation of the artwork.
It gives you control over any type of reproduction.
A reproduction that is transferring a peace of art to an other type of arts - e.g. a vehicle design or a figure of a movie to papermodel design - is so called derivative work.
Copyright holder has full control over derivative works as well.
So before you want to sell any derivative work, you have to ask a consent to use from the original copyright holder.
So you can not just start and sell them. However personal and non-commercial uses of copyright materials are allowed, so until you do not ask money for them, you can post your design.
Just to give weight to all the above, there is a plastic kit producer company, who happened to launch great starwars model kits, but without the consent of the copyright holder. They were forced to stop selling.
That's it.
So long!
laci