Hello from Chicago... is it too much rust?

[Togo-SKO]

Hi everyone, my name is Tom.
This is my first post and english is my second language so sorry for not using right terminology.

I did convert dodge van a year ago and now i am about to buy a school bus to convert it and do road trip across US.

I found a bus, it is 2001 ford e450 with 7.3 power stroke engine and 119000 miles on it. Price is $3700 .
I can't inspect this bus in person but person selling it send me bunch of pictures.
Everything seems fine, there is no check engine there is no ABS or break light on.
The only thing that concerns me is undercarrige rust.
I've seen few buses before around Chicago but those were in much worst condition due to winters here. This bus is located in New Hampshire.
i don't know what to think about it.
Here are some pictures, what you think?
What is this box that I circle on one photo?

https://drive.google.com/open?id=0B1P6kljjIOhxdUc3RVdlbFk1NHM

Thank You for any suggestions.

 

[Seriousracer]

That is the second battery box circled in red. they are always rusty. And that on isn't showing the battery so it is ok for a while.

 

[roach711]

I have a 2000 E450 from the Detroit area that has more rust than that one but my frame rails are still solid. I'd say it looks OK.