Budweiser cooler rebuild help

[dalbers]

I am rebuilding an old cooler for my brother in law and the bottom is rusted out. I started cutting out the bad and it just keeps showing up. I think i will replace the whole bottom.

The questions I have for you is what is a good way to get the curves and not just have them square?

Guy at work suggested fiberglassing it but that doesn't seem like it would hold up very well.
Thanks