Thanks everyone - for all the kind suggestions
Looks like the Bunnings PVA mats without the holes get the vote here - BUT (there's always a but in life ain't it

?) - what's the wear&tear/durability like? as in with a castored chair rolling over it etc? I suppose I can place a carpet protector mat over that area in the corner where the desk/PC is
BTW my raised floorboard (unfotunately) is chipboard - supposed to be plywood - but it works OK - might put up some pixs when it's all set up - the pier is already at work - however the continuous bad weather, clouds/rain has been ongoing the last 5 weeks or so and is delaying me slightly
Ooops! Sorry, I just noticed that I should have posted this is the "DIY Observatories" section in the first place!!
Once again thanks heaps
Cheers
Bill