I've seen tank on ebay that are already to go for that type of application. Check around if you like. As for the other plan... well... I've never done anything like that so won't attempt to offer any tips on how one should do it. Here's a bump.
Now that I would like to do, except for have a spot for the battery and maby a future bottle. A lot of work and time though, and that's not something I have a lot of, I might just sump the tank for now. When I mini-tub the back I'll probally go that rought. I wouldn't want a tank that big.