I saw this one, the well trays are removable, it's "airtight", but might not be watertight.
A number of companies market "airtight" palettes of differing designs. Some with removable trays. The small amount of air inside atleast slows-down the curing of oil paints. It's a paradox when painting en plein air
with oils. We want the canvas to dry quickly for safe travel, yet we want the palette to remain "wet" for tomorrow.
The problem with using an aromatic like oil of cloves on a cotton ball is it attacks some plastics. Lavender Spike oil might work.