Keep in mind a cargo van can be anything from a metal box with a bed to a fully decked out camper with a stove, fridge, sink, heater, AC, and even a full bathroom.
This will also be a review of the technical aspects of Camp Like a Girl and The Vanual.
Insulating a Cargo Van
The most important aspect of creating a mould-free camper is the insulation. Here is the key point: no water vapour can enter the wall cavity. With exterior metal walls, as soon as you are heating the van to the point where the exterior wall will be dewpoint, you have a serious risk of condensation and mould in the walls. So again, to keep it simple, no water can enter the walls if you plan to heat your camper when it's cold.
However, just the foam on its own will not be airtight. You can used canned spray foam to fill in the gaps if that is tolerable for you. It is not chemical-free but I have found it odourless once dry. Handi-Foam is the safest one, as it is GreenGuard Gold certified.
If you are putting the plastic covers back on the walls like Camp Like a Girl, I would silicone/caulk around those to make it airtight. The most tolerable caulking is Eco-bond.
Robert Lawson, another van owner, is trying this strategy to fill in all the gaps: he says: "I have 1-inch polyiso foam on the walls and ceilings. I plan to put Reflectix between the foam sheathing and the steel body so there will not be an air space where condensation could form. I will put another layer of Reflectix on top of the sheathing as well in order to cover all the irregularly shaped frame members."
Camp Like a Girl also uses insulation in the bed platform to keep the bed warm. Here I would definitely go for insulation that doesn't have flame retardants instead of XPS. If you are putting your bed on something solid in a camper I would cover the bed in a plastic waterproof cover otherwise it's a mould risk.
Spray Foam is going to be your safest bet for preventing mould, as the foam will get into every crevice and form an airtight layer that will prevent all moisture from getting into the walls.
The best spray foams are Heatlock Soy line at Demilic (GreenGuard Gold certified) and Icynene Proseal (GreenGuard Gold certified) (closed cell). Both are polyurethane foams, from reputable companies that are usually easy to source. It must be closed cell, which is a vapour barrier. I recommend these to healthy people who are set on spray foam. I don't usually recommend them to people with MCS because I have heard bad stories (and there are better options for most homes). However, I have an extremely sensitive client who can tolerate Demilic. In theory, they do not offgas, but if not done perfectly they do, and that is a huge risk.
It is worth considering in a van, especially if you are mould sensitive but not chemically sensitive. You can also then try and put a vapour barrier over this or use metal walls to prevent the possible offgassing from the spray foam from entering your space.
Walls and Ceiling
Metal is your safest bet unless you are putting the plastic covers back on. This all depends on what kind of van it is, as they are all different. But if you can use metal walls, that is your safest bet. For an extra layer of protection, caulk around the seams to prevent moisture from going in the walls. If you are not using spray foam or canned foam then this caulking sealant around the walls is crucial.
Sara used PVC ceiling tiles which are toxic, but real tin ceiling tiles could be used as a non-toxic alternative which add a fun look to your camper.
While The Vanual looks very pretty with its wooden ceiling, but I would avoid plywood as walls, ceiling or subflooring. There are just too many points where the wood hits the metal. If you are intent on getting this look, you would have to have lots of insulation at all the metal ribs to make sure dewpoint would never be hit. If that is possible, then you could use formaldehyde-free plywood with strips of wood over it to get the look in The Vanual.
I wouldn't feel comfortable using wood to raise the floor joists as the wood right against the metal could be a recipe for condensation and mould. Riged foam may be your best bet for floors to solve the thermal bridging there. Or else spray foam between the joists and then use metal flooring.
Different flooring materials could be considered - metal, which could be painted with different designs for a pretty effect, or covered with rugs, or Marmoleum (if you can tolerate the smell of natural linseed oil). You could also cover it with EVA mats. You could use wood if you are sure you have enough insulation underneath to prevent condensation from forming under the wood (and the wood can withstand high humidity). MgO board could be used as subflooring here if you are using Marmoleum or wood. The MgO will crack though.
Interior Structures: Bed, Cabinets
For cabinets, if you do use hardwood plywood, go for a formaldehyde-free plywood like Purebond or use solid wood.
You need fans that move air out - one above the shower if you have one, and one in the general space. My CampLite had two fans and we still have problems just with cooking humidity making the mattress wet. The standard camper fans are Fan-tastic.
The Vanual has some cool tips for solar power, wiring and appliances. If you want to go off-grid you will need solar and you will need to tolerate a fuel stove. The Vanual and other van owners speak highly of Goal Zero solar systems because of how easy it is to install. See comments in this post on others who do not like it.
The other option is to wire the van to plug into a campground plug (or modify to plug into a house), this would allow you to cook on an electric hotplate and would allow an electric heater. Using an electric blanket or pad is a good heating option to save energy.
For off the grid heaters I would go with the rooftop propane heater/AC combo that many trailers have. Though extreme mould avoiders have said these can get mouldy.
I would not use the stand alone propane heaters that go inside as they will not be safe for those with MCS.
For cooking, if you are off the grid you will need to burn some fuel to cook. Cooking outdoors is safer. Alcohol burning stoves are safer than propane. Though this won't be tolerable for many.
For a fridge I would go with a 3-way fridge that can run on propane solar or AC electricity. Unlike in most trailers propane is stored inside so this could become a problem. The Vanual recommends running this fridge on solar or the car battery.
An Overview of the Process
I like this YouTube video because it gives a good overview of the whole process and how complex it is. With a few tweaks this van could also be very suitable for a chemical or mould sensitive person.
If the insulation is sealed up perfectly by the Reflectix and tape, than no vapour will pass through. If you have a high enough R-value to keep the wood walls from getting condensation then this could work. (You would still want to use a wood that holds up well to high moisture areas).
A few materials need to be tweaked: use solid wood - no laminate or plywood, natural bedding and cushions, slats under the bed for airflow (which I think he did), gas stove may or may not be tolerable, a better extraction fan, and I would look for an alternative to that vehicle carpet.
Here is an example of one custom made for MCS, you would want to see how the construction was done.