Roof box or Tray?

2x for the tray and bag, very versatile option.

I have previously sprouted about the benefits of a wire basket in conjunction with a bag.
On our last trip to the Kimberley, I found no matter what I did in the way of strapping, the bag tended to fill up with air resulting in an irritating flapping noise. I had three cross straps and one down the centre and still the canvas bag ballooned up into an unsightly and noisy mess.
By the time I got to the Alice on the second night from Adelaide, I ditched (folded up and stored) the bag as it was a complete nuisance.
The sort of stuff I was carrying on the roof, including folding solar panel, folding table and chairs and camp kitchen, etc., all had their own covers, so the canvas bag was really superfluous and a pain in the butt to secure. Two 2ltr gas bottles in the rear corners of the basket didn't need any covering at all.

Now I tend to just use the wire cage mounted on a pair of Rhino Racks and carry stuff up top that doesn't get too impacted by rain or bulldust and just rely on the carry bags of each item.

The wire basket still needs a liner on the bottom to protect the gear being carried from rubbing on the steel mesh. This will eventually wear holes in the products individual bags or covers.

A wire basket style of carrier is both flexible in what can be stored up top and also easily removable between trips.
With the basket removed, I can fit under anything higher than 2.1 metres, so undercover car parks and other low lying obstructions rarely present a problem.
The basket is secured to the roof rack rails by four plates and Rhino nut/bolt sets.

Most Trays I have seen appear to be permanently mounted to the roof racks and reduce the clearance required for "everyday" situations.

Thanks guys. Yeah went into an ARB shop yesterday came away with same opinion. Funny, both it and the local 4WD 'Roof Rack City' had bugger all rack set ups in store so opened the websites and brochures! I like to look, see, touch before i buy lol!
I digress... Box is out. I want tables, chairs, tents etc. Bill, both shops were recommending the rhino racks with removable either wire cage, or AT alloy tray. For the same reasons you mentioned. While not as 'sexy' (quote from another forum!) as the permanent mounted platform/tray definitely more versatile.

Interested in opinions on the cage vs wt tray, and also chouce of x-bars. One recommended 2 aero-bars (with at alloy), other recommended 3 heavy duty bars (with cage).

Thanks guys

I've only ever had 2 bars, but I've only ever had a setup for the roof of a twin cab ute. A wagon with an 1800 long setup might need more.
I've had both aero bars and heavy duty rhino racks. The aero bars do the same job with a heap less wind noise when you get home. Whether you get a basket or a tray depends on your budget and what you plan to use it for. Either will do the job.
I must have a better designed bag than sand mans, a bag flapping on the roof would drive me mad also, but thankfully mine behaves itself. Have a look at msa bags, or get one custom made from a canvas place for less.
Keep it simple and as light as possible. The heavier you go the heavier you need.