[BENT_8]

Thanks guys.

Yes it is quite big and without weighing it individually, id say heavy.
The people we bought it from had quite a bit in it and were towing it with a late model Cherokee having recently done a trip to Darwin but didn't mention any towing issues despite what you'd expect to be reduced tow ball downforce.
When we got it home i started adding stuff we'd need and on towing it at highway speeds i noticed it felt unsteady within a few km's.
It was so bad that i couldn't travel over 80k/hr.
I discussed it with a few knowledgeable people and the plan was to either remove the box and return it to how it was originally, or, gradually remove and/or shift the contents forward to restore the correct weight distribution, at this stage we've gone with the latter of shifting weight as the box is very handy.
Its surprising how much crap you take with you that you dont really need.

Things gradually improved to the point where it now tows quite well and i have no trouble at 100k/hr.
Surprising what little it took to rectify really.

The plan moving forward is to have the springs reset, a wheel alignment and discuss an axle load upgrade by a company at Wingfield who specialise in that stuff.