Andy
I have a word version of the Customs declaration form, drop me an e-mail if you want it. That goes for anyone else. It is editable and all you have to do is paste a scanned copy of your signature into the last box.
The Customs form is the one you need to send customs 4 hours before you RETURN to a non customs field.
WXMAP used to let you file from there but I couldn't find the facility last time I looked. I suggested to Avbrief that a flight plan file service would be a good idea but they didn't bother responding to my mail. Ho Hum