I've build my Ford Econoline 350 extended high top from scratch. It was a delivery vehicle before I purchased it.
So it isn't a factory built class B.
I have a small Mr Buddy propane heater and an extension hose so that I can use either the BBQ tank or the small cylinders. On low setting it can heat the Van nicely. I am not full timing in it or living in it in sub zero weather. But on the high setting it would run me out of there.
You will notice these have many features such as the low oxygen cut off and it can sit on the floor or mount on the wall. It generates 4000 or 9000 btu's of heat.
I also have a brass adapter that I can refill the small cylinder (green on the right side of the photo) from the
white BBQ grill tank. Harbor Freight sells those.
What I would urge you to consider doing, if you can do it at all, is look at the bottom of this post and there is my website that is for converting a Van for week end and part time. Then find a decent used Van and begin your fitting it out. Yard sales and Flea Markets this time of year are full of summer Camping equipment and can be had cheap. Great time and place to start collecting items to fit out your Van project with. It isn't that
expensive or requiring that much in tools and materials for a Guy. If you purchase a delivery Van as I did
consider driving it around some and make sure it is solid and won't need extensive mechanical work. Then if it
seems sound find an Auto Detailing Shop who will for $70 dollars or less give it a good wash inside and out and clean it thoroughly. It will look nearly new and then you can start your conversion.
Once you are set and your Van is finished.....consider going to a State or National Park for a weekend and sleep in it over night. Take a tablet, pencils & pens, a small digital camera if you have one (or use the cam in your cell) and record the set up where you were camping. Take notes on things you wish you had and didn't. You can make a list of things to make a kit with and begin to carry with you. A bicycle rack and an old bicycle are handy to have fastened to the front of the Van. You can go out and ride around the Camping area and take pictures and in the event of a break down you can ride the bike to get help. When camping in the Van if you need to go get something you can ride the bike if it isn't too far. Thus not leaving your Camping
space.
What you are asking is easier than you may think if you take a few of these "shake down" tours. They are only trials and experiments but they will give you the experience you need before setting out on a long tour.
It will build your confidence and have you ready.
I think it would be easier and perhaps better to be building the Van while having a home. Once on the road
you won't have the home to go to if you sell it and the amenities of a garage or shop to work on things.