What kind of longevity may I expect ?

Hi !
I've bought a tank with floating lid to store my developer.
It is made of PCV plastic, has a nice faucet and a transparent window to see the remaining level.
But the floating lid has a little gap in order to slide easily, so I wonder if the air ring in contact with the chemistry may cause oxidation problem ?
I plan to put D76 or the like into it. So what should I expect ? Is it wise to cover the floating lid with Saran wrap or with gas like Protectan ?
What do you think ?
TIA !

The diameter of the floating lid must be slightly smaller than the diameter of the tank or else it won't float. That is normal. You need do nothing extra. The lid greatly reduces but does not eliminate surface area exposed to air. That slows the oxidation of the developer.