internal decals
 

anyone got any advice or tips about fitting this and painting over the back of them, about the only way I can get a shell thats a bit smart, got some orion internal decals

is there any special tricks that help fit etc

Nope, Just wash the inside of the shell well, With warm soapy water, Rinse, dry and carefully apply decals without touching the inside of the shell with greasy fingers. Paint it and you are done!