I cut my battery before I got a lipo tray, the cut was maybe 2mm deep, and it has been fine, as long as it does not cut through the hardcase into the cell.
If you want a cheaper alternative, check out the diggity offset battery tray for the TC5; http://www.diggitydesigns.com/D3_TC5...eExtended.html
You can use it with the stock battery strap and fits all lipo's (my IP 5000 fits with a little room to spare and it is the large type). It also balances my car left to right at 1350 almost spot on.
The Exotec is a nice piece of kit too, up to you.