I have a long range 120L fitted to mine. Can get just over 1000kms but I have the 1KZ (Diesel). Or 750kms driving like mad and on 17PSI.
There's plenty of pro's and cons for both, but for ease of setup get one large tank with good underside protection. Mine has been through the Simpson and various other places with buried rocks etc. Still works and goes great! Almost like a tank slider
no need for rock sliders
Got it form Opposite Lock. The standard Hilux tank size is pathetically small I know!
With the petrol it will help immensely! That is a very short range indeed. I used to get around 500-600kms for my diesel but I don't exactly drive mine like grandma either. 66L (DCab) - 120L, yours would be 77L (XCab) I think, well I think the capacity difference speaks for itself. It also sits better underneath, doesn't affect ground clearance or exhaust setup.
Also, going against popular belief, 98 octane will yield a better range than 91 or E10 rubbish. Something like 50+kms extra per fill. So that extra 10-20c/L works out cheaper over the course of a year. Something to keep in mind