Go to the Wolfenden posting - you will find several pieces of information there. Make sure you read the magazine article next to the Wolfenden article about Windmill trailer co. On another post there is information about an address, and another has a photo of the name plate.
On those threads there are some questions that you might be able to help us answer.
Around 1936 Windmill claim to have had 14 years experience, but using Trove, I can only find advertisements for their caravans from 1936 until 1938. I know they were building "luggage trailers" before that and I'm thinking that is what they were referring to when they claimed to have "14 years experience"............. what do you think ?