On my main base I use both earthen walls and a dry moat since that combination is historically accurate for a Viking trellborg. That fortress is where I spend most of my non-exploring time and is most likely to spawn a raid.

My plains base has an earthen wall without a moat because I got tired of the Lox smashing the stone ones. I have an earthen wall around their pen and access to the pen and outside the lodge is by earthen stairs. Fuling can climb the earthen stairs and deathsquitos can fly over the earthen walls but I don't spend much time there. Only to tend the lox and farm. I fill up a chest with black metal scrap and when I have a boat load I sail it back to the main base.

All of the other bases are merely portal hubs or a place to drop off stuff if I am carrying too much. They have no defenses because I spend all most no time there.