Your mention of Magna being low quality is interesting. For years I used only Magana in my vehicles. I read of expats having problems with their Catalytic Convertors and shrugged it off as nonsense. I WAS WRONG ! My wife's Rav 4 has a partially plugged convertor. She now uses Premium. magna is mostly produced in Mexico according to the forum experts. It is NOT a low sulfur fuel. Premium is produced in the USA according to those same experts. It is a low sulfur fuel and Pemex even puts that on the pumps or the signage. The Rav 4 convertor is around $300. If you have a gas motorhome with dual exhaust I bet the convertors are more like $400 each. Only 83 centavos price difference. Less than a nickel a Litre.
Moisheh