roof vent

I have two spinney roof vent thingys on my T4, Practical but Ugly they may be, but there going, I’m looking to remove and install 2 sky lights, the holes are 150mm so the roof lights will be small and hopefully unique I’m after sealed units, slimline internally, flush with roof lining, tinted...

Was thinking of adding a small opening roof vent, something like a Fiamma 28 cm square vent. Anyone had any experience doing this, even the smallest one they do at 28cm sounds quite big to me? Anyone know of anything smaller? Thanks

Has anyone everyone ever fitted a roof vent to a T4 (such as a Fiamma 28 which is an openning vent about 30cm square)? Did it cause any problems? Did it increase wind noise very much? I intend to fit it towards the rear of the van. Thanks.