Do not fit it to the back of the cabinet on most units, I did that and lived with it for a long time but its not the best way. The expensive filter (over $45) gets clogged up fast and becomes less effective all the time.
You can use a shop vac, they don't do as good a job as the ones I linked to but they work, the separator makes a world of difference, after some hours of actual use there is still nothing in the new filter but the bucket is about 1/4 full so you just dump that back in and keep going.
The inexpensive HF cabinet can be actually quite good for small job if you do the mods to it right when you assemble it. More on if you are interested. A top opening unit is better if you do big parts but more expensive and totally unnecessary for smaller stuff.