Just a thought.
If your RV is stowed on your property could you do your 4 year old’s birthday “camping trip” there, instead of venturing off with all the concerns and parameters that freezing temp camping entails? Keep the propane furnace running, cart needed supplies in and out of the house, spend the night, and have fun. The little tyke is on the short side of 4, and I’ll bet those memories will stick just about as well as if you went far afield and maybe ended up with frozen pipes out in the country. Back in the day it worked when mine turned 3, and he still talks about it. He’ll be 30 on his next birthday.
Just a thought.