The plastic shouldn't be too smooth as this creates problems with paint adhesion. Better to just fill and sand the seams, prime, put down several coats of paint and then buff those to a shine.
There was a thread, either here or on RCgroups, about how to motorize one of the Imex kits but as they are so small that they only work well in calm water. It's still a good help for general bulding, i'll see if I can find it for you.