Ok that makes sense. I'd still say the roof is your best option. And really no need to get a spendy Rotopax or Jerry can, get something generic till you sort out your long term needs.
Also, I prefer the Nato fuel cans to steel Jerry cans if you're going the 5 gal/20 L route. And FWIW 2 2 gallon Rotopax will fit in the same space a jerry can fits. So for instance I frequently carry 1 Nato can water, 1 Rotopax water and 1 rotopax fuel in my Jerry can holder on my bumper. Or obviously and permutations of that.
Agreed, This year I will probably hold off and carry a fuel can, then reassess the situation after that unless I find an unreal deal on a bumper or something before then.