I wanted to fit a Rotary Roof Ventilator but because the roof ribs are so close together all of the units I looked at would not fit between the ribs.
'Flettner' manufacture a narrow base version of their TCX 2 model ventilator which will fit, but they do not recommend it for use with smaller vans or being fitted to large unsupported panels.
Well I did fit their unit which is quite large to the rear of the roof as close as possible to a roof rib and it has worked with no problems. The roof of the NV200 is extensively braced and provides plenty of support.
I have a roof rack fitted which can create a little wind noise, but the roof ventilator seems to be inaudible and although it was not advised for smaller vans it has not sucked the side in!!.
The ventilator is well made from strong material and is very easy to fit with a single bolt fixing and has proved weather tight. However being the narrow base version the hole in the roof is not round which makes forming the hole a little more tricky.
I did email Flettner for advise about the suitability of this product but did not receive a reply which was disappointing.