I’m planning on doing rock wool insulation for my walls and poly iso for my floor and ceiling but I haven’t decided on what to do about a vapor barrier. I’ve heard mixed opinions on this so I was hoping for some insight. I have a bunch of spare reflectix that I could and probably would use but is it worth it?
A vapor barrier is designed to keep water out of your framing. That’s what it is used for. Unless you want to protect something from water inside the camper ou don’t need a vapor barrier. The van or vehicle is already water proof from the rain. I always used a vapor barrier on a floor that was wood though. Sue to it being exposed to wet locations like kitchens and bathrooms and wet shoes. So I would say vapor barrier for the floor, yes the walls and ceiling optional but couldn’t hurt to have a little extra protection if you have a kitchen bathroom area. Just my opinion. Hope it helps.
Very helpful, thank you!
How did the rock wool insulation work out? Would love to hear from someone who used it first hand.
Here in Canada it is VERY necessary to have a vapor barrier, as the winter will definitely give you moisture and mold problems on the inside.
I personally went with spray foam as it seals, insulates and provides the necessary vapor barrier. 
Greetings!
I don’t have vapor barriers, or any added insulation… Lots of dry heat combined with enough ventilation is the only combination that’s ever worked for me.
I want the air to get to the inside skin of the vehicle, to evaporate any condensation. This was the original factory scheme for both my van and my bus. It has worked very well for me…
Cheers!
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I don’t think it is good idea to add moisture barriers between your interior and exterior walls. The exterior walls of you van is already a barrier to moisture. If you add an additional moisture barrier on the inside, you are creating a suituation where it could trap moisture, where it cannot properly dry out, causing mold and other problems.
A better design is to construct your interior walls to be breathable and use a insulation like Havelock Wool, which is hygroscopic and can easly absorb moisture and release moisture instead of trapping it.
Hope this helps,
-tom