leave the oil in the tank. You need it to lube the RV cavity. As for gas in lines, if that worried, then pull the gas line at bottom inlet of carb, and drain, along with undoing the inline filter. Then let motor, re-prime the system.
As for oil for premixing, make sure its a "premix only" oil, and with the API-TC somewhere on bottle. Found cheap sh** at gas stations, when I had premixed boats...didnt care, as long as its premix oil.