I am planning on buying the Givi tubular racks (Givi stock# PL532) and mounting the Sears medium or large boxes to them. Who has experience with this? Do the Sears boxes mount great to the racks, or do you have to use the mounting plate, or what? Is there a difference between the medium and large Sears boxes, does one mount easier than the other? Also, anyone know of a way to get a better deal on the Sears boxes? I bought the large last year for ~$50, now the medium is selling for ~$59. Any coupon codes, etc?