German panzer protective coveralls?

[collector15]

Hi everyone, I´ve acquired this coveralls marked by "RBNr" number and by "Gr I" (I think this is the size marking). I´ve been searching for some info and I´ve found some information about german one piece panzer coveralls. I would like to know if this example is something like that or totally different piece of uniform. Have You ever seen something like this coveralls? Many thanks!