You’ll get more helpful answers if you clarify your situation.
Will the Caravel
be in use?
We assume you are talking about the fresh water system. If not in use, it won’t hurt to leave the antifreeze in; nothing will grow in that.
When you do go to use the trailer, a lot depends on the quality of the water and the turnover. Use good water and keep it moving. Drain by gravity between stays. In Florida, we keep it full as a backup water supply during hurricane season and have never had issues.
Bleach is OK for sanitizing, but can degrade plastic over time and leaves an unpleasant taste.
For the gray and black tanks (a combo tank is essentially a black tank), drain them and flush well after use. Keeping them “sweet” during use is key. Settle on an effective additive. My wife has used several, including the tablets from Walmart and a liquid version from Amazon.