Hi,
I just discovered that Trimble completely redesigned their 3D warehouse and removed Collada files. [:(]
Actually, the Collada files seem to have been replaced by KMZ files (see this model for example) which contain a Collada / DAE file. Thus, replacing .kmz extension by .zip will let you import such files in Sweet Home 3D. To make it simple again, I might add .kmz extension support directly in a coming version of Sweet Home 3D if it's supposed to always contain a .dae file as it seems.