Rossboxing.com did a huge guide on them, if you can't get a bag up the only way to get it to even reseble a bag it to fill the base with cement or conrete and do it in layers so it compresses, even then you have to have a high friction floor other wise it goes all over the shop.

Once you've got it to stay roguhly static you just don't get the angles to throw shots at or the swing of the bag adding extra resistance and moving around a static bag is not a good way to develop footwork.

If you cannot get a bag bracket up any in your house then this is what you want:

[img width=525 height=700]http://www.protecboxing.com/acatalog/CORNERMAN.gif[/img]
www.protecboxing.com

more than a regular bracket and you'll have to buy weights to place on the legs (I think, it may come with some and you probably have some) but its well worth it.