I always clear coat after the decals. I put several coats on, sanding carefully between each coat to remove the step of the decals. Need to be very carefuy not to sand through to the decas.
I use Tamiya TS-13 staight fom the can and/or Gunze clear through an airbrush. Being lacquers you need to be very careful to only spray light mist coats initally so the strong slovents won't eat the decals. And it should go wthout saying that the underlying paint has to be lacquer too if you wish to use a lacquer top coat. It is possible to mix different types of paint but do lots of testing first.
After that a final sand down with some very worn fine sandpaper, polish with compound and finaly some carnuba wax. For me the last three steps give a more realistic finish than just leaving the final 'wet' coat shine.
The Renaisance doors are simply cast from the Tamiya doors if IIRC.