You are absolutely correct - the maximum width to register any vehicle (including a trailer) in Australia is 2.5 metres (98.4").
If the trailer or load is wider than 2.5m, then you can obtain an oversize permit which will allow you to tow up to 3.1m wide with the appropriate signage and flags. Yep, it's all a bit vague... more information is in this link. Even though each individual state has its own motor vehicle laws, as far as width goes, they are pretty consistent.
http://www.vicroads.vic.gov.au/Home/HeavyVehicles/RouteInformation/OversizeOvermassVehicles.htmOff the record, 102" is pretty close and most people would probably register and tow this without a permit! Little or no chance of getting caught - not many police carry a tape measure!