Hows the gap between the plasterboard and the breeze block? Thats really area of concern so filling wtih resin like sigma said above would be good (if you have something that can inject it). Can you get to both sides of the breeze block? If so you could bolt a back plate on one side..
Personally if you've got a wooden beam going across the ceiling that is solid (maybe a picture?) I'd just get a small bag and hang it from there. My bag is 5ft and pretty much spot on:
Personally if you've got a wooden beam going across the ceiling that is solid (maybe a picture?) I'd just get a small bag and hang it from there. My bag is 5ft and pretty much spot on:
