If you search this board for "hot glue" (with the quotes), you'll find this has been discussed many times. Some people will say it is fine, others that you should never use it.
I believe it is non-toxic, but also that it is not designed for use under water.
Whatever, you read your threads, and you make your decision.
Solubility in water: Insoluble, material reacts to hardened mass for non-hazardous waste
Hazardous Polymerization: May not occur
About the only thing the data sheet says is not to eat it while hot (man that would hurt), subject it to cold temperatures, subject it to high alkalinity, or breathe excessive fumes.
Like Lateral said, do some research before you make a final decision. Thats just my $0.02
the hold won't be great under water, but as long as there isn't much pressure on it, it should be fine, just watch the hot glue gun on glass (that would suck the crack the tank)
Buy some plastic channelling from your local diy store (mirror runners) and purchase some plastic condensation trays from you local aquarist shop, secure channelling on inside the front and back panes and cut the condensation tray to suit and slide the dividing sheet into the aquarium.
Regards
BigC