Tips to prevent chafing when exercising?

Any tips to prevent chafing when exercising? I have found if I do the treadmill for more than 30 minutes, I chafe under my butt cheeks, like where my underwear line would be.

I have even tried not wearing undies but it still happens. I like to do a really good 30min workout to see how far I can get and then I spend the rest of the time walking or power walking.

At night I’ll slather on a bunch of aquaphor and loose sleep shorts and it’s better the next morning.

But if I could prevent it that would be great.