A logical definition of a 4 season camper would be a camper that a person could use all year long regardless of the weather or the temperature.
However, the RV industry doesn’t have a standardized definition for a 4 season RV or 4 season camper, so manufacturers are free to use the term as they wish.
This causes confusion among potential camper buyers that don’t have the background or knowledge with regards to the weak links in the camper for cold weather use.
The bottom line is that the manufacturer and salesperson can call any RV a 4 season RV or even a true 4 season RV with no repercussions. The main concern a customer should have revolves around water, and how to keep it from freezing.
A typical layout for a camper will include a freshwater tank and fresh water lines. You have a “black” tank to hold wastewater from your toilet (unless you have a composting or cassette toilet which does not require the holding tank).
You also have a “grey” tank to hold the wastewater from the shower, if applicable, and the water from all sinks. The terms “black” and “grey” refer to the water stored in each and not the color of the tank. The water system will also typically include a water heater and a water pump.
When a camper is not engineered for use in cold weather there will be components of the water system that will freeze. To keep the water system from freezing it obviously needs to be heated. For some helpful tips on this, check out this great guide on how to protect your RV from heat loss.
While there are a few ways to heat the components of the water system, the only way that really works is to heat it all with forced air.