Cool, if yours is a 72, it should be alot easier than my 46 because I think the bow is actually less and spans a greater distance. All I did with mine was cut two rings out of MDF using a template traced from the top of the tank..
In the above image you can see the ring that sits on the bottom ( looks like an upside down "U") and the one on the top is complete ( looks like a "D).
Then I took 1"x2"s and cut them to the height that I wanted and made a bare frame. Sorry I dont have any pics of this part but it looks similiar to wall joist.
Afterwards, I just used 1/4" Oak sheeting and skinned the sides and the back....
Then I took a full 2x4 sheet of the Oak, which already had quite a bow in it, and ran a bead of glue along the frame work where it would sit. Started on one side and tacked it down with 2 finishing nails. Then I used clear tape, and while my wife put a lil pressure on the sheet and bent it down to meet the curve, I put the clear tape on real tight and let it set overnight till the glue dried. I also tacked it in several places with finishing nails.
In the above pic, you can see the tape still on it while I test fit the canopy on the tank.
I dont have any pics of it now that it is painted and finished but, I caoted the entire insides with a thick layer of Killz to seal the wood and then topped that with several layers of Gloss White Enamel in a spray can. The outside was sealed as well and painted a Satin Black Enamel to match the stand.
I hope this helps you out on yours and post some pics with your progress!!
EDIT: Im such a dolt, after looking through my Album I found one pic of it finished..
Hope that helps!!!