If you’re looking to rent, a friend of mine used and recommended this place:
Mercator 2395 2302.
2/F, 57 Sai Yueng Choi Street South, Mongkok, (Mongkok MTR Exit D3), next to Body Shop.
Need to be a ‘member’ to rent but that sounds to be a low threshhold eg. with $200 purchase or some negotiating.
Tent (3 or 4 pers) $60/night.
Sleeping bag $60/night.
Also try this thread: