I built a floating base and no Purge. A bit after building House for my wheel nearby, there was a purge on the land based building.
A floating base has some advantages if you use pillars and build a bit above the water level.
People can not climb your walls. This is the first base where I have windows and feel safe.
If you build far enough from shore, Orbs cant reach you.
Underwater weapons can damage your pillars, but as long as you build multiple supports, it will take a lot of work to bring down your base.
Gods will destroy you.
Jars still can take down Pillars, but as with weapons, it will take quite a few jars.
Trebs can wreck your base.
Also, taking out pillars/walls is useless to gain entrance to the base since it still gives them no way to actually enter your base. The only real way in is to take out the floor while leaving the pillars intact. Again, Treb is your answer to do that. Mainly though, they will have to destroy almost your entire base to get your goods. That could be a good thing or a bad thing…
Basically, you will make them work a bit for your goods. Not impervious, just hopefully enough work that raiders move to another target.