1. This is real tiger country, if you crash here, we may never find the wreckage.
The weather is your enemy because you are using a slow machine. Furthermore, going from Mansfield to Gippsland you will encounter at least TWO separate weather systems, maybe more; for example hot inland concditiond with turbulence around Mansfield, a seabreeze front on a Gippsland afternoon and thunderstorms over the ranges where some mixing occurs. Then there is sea fog (yesterday around Portsea) and smoke, haze and dust north of the ranges.........and that is all on a settled day.
Now if you are in some sort of bullet like a Cirrus or Bonanza, you just need a short window. You can get high enough 9500 - 10000 to pretty much see the whole route. Furthermore, at 160+ knots, a 10 knot seabreeze sprining up or a thirty km diversion around a thunderstorm is no big deal, plus you have an autopilot and excellent navigation gear.
BUt you are only doing 65 knots aren't you? That means a ten knot seabreeze can ruin your day and forget about 30 mile diversions, you dont have time or fuel so your route planning needs to be very different and by the way, dont forget density altitude; if you have to land some where high you will be walking home. The advantage? At 65kmots its prettyy hard to inadvertantly go from VFR into IMC.
My bugsmasher is somewhat in the middle. What I would do is treat such a project as an adventure with very wide time frames and a very flexible itinerary - like the old sailing ships - they never contracted to go for example "Melbourne to Sydney", the contracts specified they were going "from Melbourne in the direction of Sydney".
Now if you can set out with an open mind about where and when you might end up, plan your trip as a succession of small stages that only nibble at tiger country with go/nogo points between them and lots of alternates you will have a wonderful tme. Just dont get caught on one side of the range with a long slow trip home in darkening weather.