spotted this over on the Earlybay . they are cheap and seem very effective http://www.ebay.co.uk/itm/AFO-Automatic-Powder-Fire-Extinguisher-Ball-Home-Office-Boats-Caravans-Cars-/110910196287?pt=UK_Fire_Extinguishers&hash=item19d2c34a3f#ht_3147wt_1139
Or these, i always thought firetec was expensive http://www.fireprotectionshop.co.uk/Details.cfm?ProdID=185&category=&secondary=59
Yes I've got my firetech but if I'd seen those balls before I'd have had a couple of those instead. The videos are really impressive.
In fairness they work in a different way and will not be as good as the firetec type system I would be worried about the glass vile getting damaged with the vibration.
I quite like this one: http://www.ebay.co.uk/itm/Classic-VW-Fire-Engine-classic-trailer-/140805741375?pt=Automobiles_UK&hash=item20c8ad1b3f#ht_1446wt_1396
What are the differences between this http://www.fireprotectionshop.co.uk/Details.cfm?ProdID=185&category=&secondary=59 and the firetec ones http://firetecuk.com/pages/en/firetec-products.php
The Firetec has a pipe that runs from it which melts in a fire & only propels the material at the point of the fire, the other unit has a vile that breaks & sends the material everywhere. The Firetec is a better unit. I have both