It's really not too difficult in a Class A if you also have diesel heat as that warm water is also circulated throughout the wet bays and they will stay toasty warm unless you use too many electric heaters inside the coach preventing them from doing what they are designed to do. If your electric is free and plan to use a number of electric heaters inside the coach then you need to add supplemental electric heat where your plumbing and holding tanks live. For me (a Winter in Detroit) that was 2 separate 100W light bulbs to keep warmth on both sides but there are also some small 200W(ish) electric heaters which could be added. I bought a "weather station" with a remote temp. sensor which I left in the bay to allow easy monitoring.
If you have propane heat it also heats the bays but tends to burn a lot of fuel to keep everything warm so using electric supplements inside and outside becomes more important for cost savings. If you have to pay for electric at the campground then you will need to find the right balance between where you want to spend the money but you are going to have to pay.