HI Olly

I've simply used Car-Plan Acrylic Plus formula Car sprays on my Fireboat, Satin Black for the Hull, Grey Primer for the deck & Cabin sides & Gloss White for the Cabin Roofs. I have however used clear varnish on the rear well and decking between the Fore & Mid cabins ( probably not true to scale but it looked right to me! )

If you don't want to leave the Grey Primer I have overcoated it with a clear satin spray on my seaplane tender which also looks OK ( just trial the two sprays together somewhere else before using on your model! )

Good luck
Chris