When we got Helga, her previous owner Charlie had already changed the bathroom sky-light to the fan version but hadn’t got around to wiring it in.
I did this last weekend and when you turned it on it sounded like a jumbo jet taking off!
In our old van, we had the bigger fiamma vents which had a sped control so you could have them on slowly at night, sucking the warm air out without the noise.
I found this variable switch for £8 on amazon https://tinyurl.com/y3f95mns
Initially I wanted to install it in the cupboard and have just the knob coming into the bathroom, but the shaft was too short so in the end it had to live on the wall.
It works well with a good range of speeds which you can see on the video (this is a link to my Onedrive account)
https://tinyurl.com/y2gumzop