What's the wood on the undercarriage treated with?

I've got a 5x8 woody and I noticed that the wood underneath the trailer has a white coating - is that roofing sealant or just an exterior paint? The reason I ask is because I'm not sure if it needs to be maintained over time with extra coatings of sealant/bed liner/etc. I want to make sure I'm taking great care of my new trailer :) Thank you!