Since the bottom has no insulation this...
Since the bottom has no insulation this bag can't be used as a single, correct? It's not like zipping two bags together.
Um, not exactly, no. It's one big honker bag with two pad sleeves (the sleeves are the uninsulated bit on the bottom.) If for some reason you had two pads and wanted a really huge not very heat efficient single bag, you could use it solo. If you don't have both pads in it though you'll have some SERIOUS draft and conductive heat loss issues.