I was down at Goomburra last weekend...the shady creek running past Poplar Flat & Manna Gum camping areas is still flowing.
Campsite info here.....
http://www.nprsr.qld.gov.au/parks/main- ... _goomburraThere is a water tap at both campsites, but bring your own just in case.
You can check availability/book campsites here... in Location box look for 'Main Range N.P'.
http://parks.nprsr.qld.gov.au/permits/; ... 1588268428 Same site for remote camp bookings...look under 'Main Range Remote camping" just in case you change your mind & head to Teviot Gap.
Should be plenty of room to camp next weekend.
Not sure if Laidley falls on the way to Mt Castle is still running.
Don't rely on it, take water, it's a dry ridgeline walk, but the views are great.
Have a good weekend. Champion_Munch