how to fix this trunk?!

If you can find one for cheap, i would replace it.
The dents aren't that hard to repair, so you really aren't stuck.
I would probably just repair it if the seams are good and not bulging from rust.
A stud gun is the ticket, and you can use it on other projects later.
Investing in tools is a good choice, it's the gift that keeps on giving! lol