Well, just owning a home in France does not give you any special right of entry but if you just wish to continue to enjoy your 2nd home as a 2nd home I don’t think much will change. You will still be able to visit for up to 90 days at a stretch without having to formally apply for a visa, although you might need a little more paperwork when you travel and you might need to sign up to ETIAS when it gets going.
If you wish to “secure your rights to reside in France full time in the future” then the only option is to move to France now, before Brexit.
Then either be working or be able to demonstrate that you have sufficient income as an “inactif” (not working, usually because of retirement), be registered with the French tax authorities, be paying any income tax and any social charges due, register your vehicle, make sure you have health insurance covered and make sure all of that is documented.
Then you will be in a position to apply for a Carte or Titre de séjour which will guarantee your right to reside in France, though you will have to have lived in France for 5 years to get a permanent CdS (this length of time might change post Brexit).