Flettner do a narrow base unit that would fit but only for their latest model. Unfortunately they do not recommend this unit for the smaller vans ie NV200. The older 2000 series vents are to big to fit the trough width of the roof ribs! So a company who claim to be the leaders in the field are not on ball. Ps. Have mailed them had no reply..This is on my to do list, as it can get very wet in the back with condensation.
I haven't looked at roof yet, do you know what diameter the gaps are?
I have seen nv vans with roof vents,so can be done.
Many thanks for that information regarding the narrow base Flettner ventilator. I will give it a go. I could not see any real problems using it and the NV200 roof looks well braced. Would have liked some responce from Flettner.I fitted the narrow base flettner vent to my nv200. I know that they dont recommend it for smaller vans, but its been fine.
Fitted it to the rear corner of the roof (more stiffness/less vibration).