Many of these smaller buildings I group together into a scene mounted on a removable base. My favored method for attaching this type of base or individual building to a module is to put 2 or more 4-40 screws through the base and extending long enough to secure under the module with nylon standoffs as shown in the October 2010 post Attaching Buildings.
The biggest advantage making smaller scenes on removable bases is that all of the work can be done comfortably at the work bench. The problem is what to do with the long screws that stick out of the bottom of the base.
At first I used rolls of tape but I found that not to be very stable.
The better solution was to build up a little platform from scraps of wood and then drill holes that match the screws.
Here is this platform in use on the work bench recently while I was working with the Green Max stores.
Notice the black markings on the platform. The holes are marked to show which ones to use for each of the removable bases so the same platform can be used for many removable bases.