It depends on the size of the louvre frame you have. I had 2 windows, both different sizes.
Have a look at this:
http://forum.earlybay.com/viewtopic.php?f=4&t=62620&hilit=Double+louvre" onclick="window.open(this.href);return false;
If it's the larger frame, it uses a standard side window rubber & fits pretty easily.
I bought the other seals from:
http://www.vintagetrailersupply.com/Jalousie_Bulb_Seal_10_Pkg_p/vts-525.htm" onclick="window.open(this.href);return false;
http://www.vintagetrailersupply.com/Jalousie_Header_Seal_p/vts-386.htm" onclick="window.open(this.href);return false;
http://www.vintagetrailersupply.com/Jalousie_Pile_p/vts-333.htm" onclick="window.open(this.href);return false;
There is a rubber / pvc trim that fits around the outer edge of the frame that makes it sit better in the window seal, I bought a length of that on eBay - goes under rubber or pvc u channel I think.
Whole lot inc postage was about £30
The westfalia seal kit doesn't fit, so don't waste your money.
Took me ages to find those links, mainly with thanks to a guy on the Samba.
Shame the main uk supplies don't stock it!