Looks great, arjunrc.

I have a couple of very minor suggestions:

1) Double over the elastic at the ends. This will double the strength at the critical point where the screws go through it.
2) Turn the elastic up at the points where the screws go through it.

At a later time, you could also sew a piece of Velcro onto the ends of the elastic, which would reinforce it even more, and give it a little more adhesion to the Velcro in the Tumi. With Velcro on the ends, it won't rotate around the bolts as you use it.

Putting together a really useful mod like this is a great feeling. And although you got some ideas from us, the final details of it were all you.

I love it when a plan comes together!