This is what you need
Weld-On #40 2 part Plexiglas Acrylic glue
Weld-On #40 2 part Plexiglass Acrylic glue is a clear two-part, reactive,
high-strength cement for bonding all acrylics to each other and to polyester,
butyrate, PVC, styrene, wood, etc. If you have seen those "invisible" bonds in
acrylic plexiglass aquariums - this is the adhesive to use. Also excellent for
laminating plexiglass pieces together, and to other materials.
You can get it at
http://www.rplastics.com
Also I wondered about using halogens...but they are way too hot. For my nanos I
stuck with Power compacts.
When you redo your tank...Get an 70mm or 80mm computer fan off of ebay and
mount it in the canopy..its super easy to wire it to a 12 volt 300ma adapter. You
might also want to cut a vent in the top of your canopy to get some of the heat out
from the halogen. The fan will help keep the water temp stable.
Or you can go here and get a Acrylic nano cube for a really low price...I think one
your size is about $25 plus shipping.
http://www.glasscages.com/