Similar to those mentioned I use Rust-Oleum "Crystal Clear Enamel" in spray cans. I've gone through probably a dozen cans at least over the years for a certain project. Each board used to get 2 wet coats, but now I put on 2 wet coats, let them dry, and put on another 2 coats. Both sides. Old boards that came back don't show any problems, and they are in relatively harsh service: high temperature, low temperature, high humidity, dust, etc.
I clean all the boards in water with a little Formula 409. Dry thoroughly. Cover all connectors. I use empty connectors with tape over any wire entries. Other things I cover with caps of various kinds. The boards are elevated using stand-offs. It's similar enough to Humiseal 1B73 for my needs.
Before I did this I coated several test boards. No corrosion issues, etc. The only damage is that some of the inspection markings dissolve slightly in the solvent.
Give it about 24 hours to cure. Spray it outside.