You can't go far wrong with Netflights they are usually around the cheapest but have alook around and see if you can beat them.
Just checked price and they want £339 less 5% Quidco = £322
They want £69 to upgrade to Platinum/Gold this includes a tank of gas and additional drivers(no other difference) a Dodge Grand Caravan has a 20 gal tank, at $4/gal (http://www.orlandogasprices.com/GasPriceSearch.aspx) thats $80(£50) so you are paying approx £19 for convenience of returning the car empty of gas and additional drivers if needed. For that price I would pay it, just to have DW included for emergencies.
Thank you for your advice I went through quidco to net flights and paid for the extra insurance all in all I paid £393.12 before the 5% cash back. So for the ease of no fuel stop and the both of us as drivers it was worth it!
Also it is with dollar so can I pre-book online so I can go straight to the garage for the car or will I still have to go to the desk?