Ok - presure is on - thanx GGPatrol.
Traveller has raised some pertinant points.
Use this basic map as a starting point:
http://parkweb.vic.gov.au/__data/assets/pdf_file/0004/313168/Park-note-Alpine-NP-Valleys-and-bluffs-around-Mansfield-and-Whitfield.pdfIf you are going in at Easter from the Mansfield end it will be busy around sheepyard. There will usually be room somewhere upriver, 6 mile, 7 mile or 8 mile flats, before Brocks Road leaves the Howqua river and heads for 8 Mile gap.
There are further camp areas in the Uppper Jamieson, Upper Jamieson Hut - steep access, not CT country to get in to and out if it gets wet (damp even) , as well as a river crossing that is treacherous when the Jamieson river gets up.
There are other camp areas in the Upper Jamieson as well tho, where the Mt Sunday Road heads of to the south. Usually quieter in there.
You could base yourselves for the first few days around there, and do short trips up to the Bluff and Lovicks hut, but bearing in mind, if you head to Wonangatta then, your next fuel stop is Dargo. Id go for a refill back to Mansfield (30k for Sheepyard) before heading to the Gatta.
You would access Wonanngatta by traveling up Brocks Track (used to be called Road) over to Mt Howitt. Then down Zeka Spur to the Gatta as described by others. You will be going down, not up, but still can be rough going and spinjcktjer clenching if in the wet with a CT on the back.
From the Gatta, then say 2 hours running out to Dargo for next fuel. Basing yourself at Talbotville will give go a base to do your other trips with access back to Dargo for fuel.
So, IMO take a spare jerry for each if possible. Your fuel tanks should be enough to get you from Mansfield thru to Dargo, but bear in mind you will chew thru more with the CT.
If you want to take the CT, Id be making sure the weather forcast is clear - no rain expected for the time you expect to be travelling thru the gatta.
PM me if you have any other queries.