Have you ever cancelled a trip and forfeited your deposits?

Yes. We often stay at state parks in general (and for at least half of our snowbird winters), and the canx policies are straightforward in writing. Private parks usually spell out their policies on their website or with a deposit confirmation.

I don't object in the least to paying if I have to cancel regardless of the reason. Canx fees help keep people from booking up limited space in multiple campgrounds while they make up their minds for sx months where they'd like to stay.