Cargo vans are the worst possible choice for camper vans for many many reasons. They cost the most to convert, they cost more to heat or cool, they get worse gas mileage, you get far more road noise no matter what you do, ventilation sucks even with multiple roof vents, and most people find that living without windows all the way around is just plain miserable.
A mini van would be much better in many aspects than a cargo van, but there is still a better choice. Full size extended length passenger vans give you the best of all possibilities. Windows for a better view and ventilation, without the need to cut holes in the roof, they’ve usually been better maintained, and the safety standards are much higher, the interior is already factory finished, so you just need to remove the rear seats, they typically get much better gas mileage because they are geared for highway use instead of city use, and the list goes on and on.
After many years of full timing and many vehicles, a cargo van was absolutely the worst, and the most expensive of any of them. All of my other choices were much better, small RV’s, smallish shuttle buses or school buses, and passenger vans offered the best experience at the lowest costs. I currently have a high top extended body 15 passenger van that was originally a hotel shuttle. I simply removed the rear seats and moved my new camping interior in. It’s old but reliable, for a total cost of under $1500 for the van and the interior, including a super comfy sofa/bed, double dishpan sinks, a stove, an ice chest, a bucket style toilet, and a weed sprayer type shower, a comfortable swivel rocker/recliner, heating, cooling, and reliable power. No solar panels, roof vents, or holes in my roof. No 12v fridges, and no propane anything. I charge my house battery while driving mostly, by generator rarely, or by shore power almost never. Heating and cooking use kerosene, as well as occasional mood lighting. Everything is portable (but secured), so it can be used either inside or outside as weather, location, and my mood warrants. Without solar panels, I can enjoy parking in the shade during the summer, and am not reliant on the weather to supply me with power. Everything is extremely simple and uncomplicated. My thermo-electric bed both heats and cools, as do my seat cushions. My 12v swamp cooler can keep my whole van comfortable even on the hottest and most humid days.
I choose to live in my van, not out of it. From the coldest days of Alaska & other northern climates to the hottest days in the south, my van is a comfortable retreat inside, and this is with no added insulation or window coverings. The solution isn’t insulation, it’s simply having enough heating and cooling power to keep you comfortable. Lots of opening windows for superior ventilation is also a huge plus. A single under $20, 10" 12v fan gives me better ventilation than two $250+ roof vents with fans ever did. I don’t use an inverter, all of my appliances and accessories are 12v, fuel powered, or dollar store battery powered. If I happen to be somewhere with shore power, I have an extension cord with an outlet strip, and a battery charger that I can also use with my generator, so I can have full power while still charging my batteries.
It’s all about choices. Choose wisely and life will be great, choose wrong and you’ll have never ending headaches until you get it right.