Check out small 'pellet' stoves
Some people have installed them in class B, and DIY van conversions
30 days might as well be full-time
You have to have substantial battery bank and a way to recharge
If primarily solar it need to be able to do 24 hrs of power in limited daylight hours
Replace Over night use while supplying day time needs
Unless you want to hitch up and move to the power pole during rainy days you need to have a generator on hand, you might get lucky and not use it very much
But you do need that option
I would really hate to drive 60 miles from Sequia NP to a KOA , in the rain to get shore power and charge my batteries
Once you get to the national parks
You will find that most have frequent rain
All the mountainous and green ones do, including the grand canyon and the parks in Utah like Bryce and Zion etc..
The Northern States, eastern States, Midwest etc..
Death valley and the desert parks are the only dry ones, and even they can get thunderstorms
I grew up in the Midwest, summer time is full of thunderstorms, several times a week
What they consider a drought, would be a flood here in southern Ca