Sure, you can use them for interiors. You can use them to paint whatever.
This Mack Bulldog was painted with them. Flat gray cab (with a coat of Testors "Transparent Window Tint" to give a sort of dirty, grungy look)... chassis with a very dark gray (almost black) metallic, interior, engine, wheels... everything! (except the bed which is scratchbuilt of real wood and stained).