Sprite Continental 450 - where is the VIN?

I have just joined the club, but the only way to complete registration was to claim that I do not have a caravan. I actually own a Sprite Continental 450, but all my efforts to enter the VIN were thwarted.

I first tried all my paperwork, where the user manual mentions 1991 in the title. I then looked in the front storage locker, around the A-frame and around the door entrance.

I did find a number engraved on a couple of windows but, entering it, I was told it was invalid. That is either an eight-digit VIN, with the three '8's looking strange, with the numbers being split into two parts. So I decided these may just be separators and so tried entering a five-digit number instead.

Can anybody help? Thanks.