weight restriction for GQ

don,t know the legal limits but in 2005 myself and 6 other blokes
3 dirt bikes and one other 4wd did a trip down the CSR i carried 140 lts, 3 swags , and a 2nd spare wheel , 2 bike tyres on the roof , yes it was heavy but if you take it carefully you won,t have trouble .
mechpete

I would not advise putting that much weight on the roof of a vehicle, especially doing the CSR. It is better placing heavy items as low as possible to keep the centre of gravity low & keep the vehicle more stable. A roof rack should only be used to carry light items. Cheers.

I would not fit a bladder type tank to any vehicles roof & even if it is baffled the surge will be real bad. If its a blister welded type it will only split in the seams sooner than later so make shore it is/has internal hinges on edges as this will help its life,they are tough but can chaff easily & normally tear in the hold down points,(eyelets, D-rings etc) I have imported/made & probably sold more than most & have used & sold since Mid 70's manly in fuel cells I use them in my Boat but never in my 4wd
regards Vince

from memory its about 200kg, but would be dependent on the type of roof rack mounting (full length rails)
As others have said it'd be better to mount it low.
A mate has a grey poly tank under his ute - a lot more heavy than a caravan tank, and we measured it up, should fit in the cargo area of a gq - its 110mm high, and holds 80 litres, all you'd have to do is make a false floor, then just get a space case for the roof rack and stick all the light suff (clothes etc) in it.
Thats my plan anyway.