I've wired up many flourescents in garages and they only take a 240v feed into a transformer, so I reckon you should be able to bypass this and go straight in on the 12v side.
B&Q do excellent 1.5m flourescent tubes in a holder at under 9 quid each - they're 58w but you can get lower wattage ones if you want.
Or just get 12v ones from somewhere like TowSure - I've used them loads of times for trailer parts (rolls eyes) and they're both cheap and very quick to post stuff out.
Awning Strip Lamp C/W Plug (13wt)
Twin tube light 13" long with 15 ft. of cable and crocodile clip type connectors. Comes complete with magnetic discs so it will stick to any metal surface. Has two 12 ft. 8 watt fluorescent tubes that give a 16 watt illumination.
£12.75
http://www.towsure.com/default.asp?t=480&p=0&d=33