I use a 35 gal galvanized garbage can on my dust collector along with a commercial plastic collector top.  For a quick and easy seal between the can and the top, get a length of 5/8" vinyl tubing the circumference of the can, slit the tubing lengthwise and run it around the top rim of the can.  The vinyl is soft enough to conform to the minor irregularities and just a little sticky with the polyethylene plastic top.  Cost: less then $1.50.  Time: less than 15 minutes. - Kerm Jensen