I'm asking this just out of curiosity.  When I'm out camping at a state park and plugged into the 120 Volt 30A Shore Line  at our camp site,   Is my camper's breaker box /  power box continuously putting out a converted 12V DC line to power my 12V DC ights, water pump, etc.   or is my external deep cycle battery powering all of those items and my camper's power box just occasionally kicking on  to keep the deep cycle battery charged to do those tasks ?

Just wondering

edit *   Camper is a 2011 Coachman Spirit of America with an Atwood Power Center

Really depends on how your system is wired or set up.

If it's plugged into shore power, it should basically be running off the power supply. Now the power supply is also wired to the battery, so they're both tied together. But the power supply is putting out more volts that a static, charged battery, so you're technically running off the D.C. From the power supply, not the battery.

The AC power is converted to DC through your trailers power panel. Everything on the 12v side is running through the converter, everything on the 120v side is, well, 120v. Your power center should be controlling the charge rate to your 12v battery bank as required to maintain a proper state of charge.