I use KF 1450, it's an acrylic varnish for pcb, it's solderable, transparent or green. The varnish is very resistent and protect from shorting, oxidation etc. Easy to use.
Another way to make the job, the inconvenient is that you have to protect the connectors otherwise you will have some problems, because the spray is very volatile, the varnish go everywhere on the board!
I think your solution is better if you don't have case.