I could be wrong but I do not believe that putting a 30 amp main and 2 20 amp branch circutes would constitute an overload on a camper that will not have an air conditioner and was installed in a panel that is rated for 30 amp.
There is a easy way to check the opporation of the breakers.
It is down low front wall. 159 bucks 35 amp main + 5 a/c circutes and 6 d/c. It is also a charger and converter with a thermostaticly controled cooling fan. Probably see something similar in mnew medium sized pop-ups