Metal for patching an M101 tub?

[Quieroacampar]

I have inherited a trailer from my parents. It was used for all sorts of hauling my whole life. Camping, hauling motorcycles, runs to the dump, etc. it's in need of some repairs, including some spots that have been rusted through. It was always stored leaning forward and water would gather in the front, so that's where the flaky parts are. I figured out that the tub is an M101 but the frame and axle are not original. I have a friend with the skills and equipment To do the repairs ( I have neither, but will be doing as much grunt work as possible). What I wanted to know is what gauge/ type of sheet metal should I look for for patching the spots that will need to be cut out?

Posting from my iPad always seems to rotate photos...

 

[98G]

Cut a chunk out of one of the bad areas and measure the thickness. My best guess says it's going to be pretty close to 11ga.