Do a google search for corrosion inhibitor and you will find many options for spray on materials. I use Corrosion X for my airplane but there are options at the local auto store from CRC or LPS and others. They work great.
If it is running good then I agree with the others and don't do anyting at all. Just drive it and enjoy. What I would do is occasionally redo the compression test and monitor it.
I have several of the Schumacher 6/12 volt charger maintainers. They all work great for several years now. The first one I bought only cost about $20 but they went up in cost over the years to where the last one cost me about $30.