New, and helping someone out.
 

Hello!

My girlfriend's grandmother has a 1970 Camaro RS. It has a bunch of surface rust in the trunk under the mat (luckily, the rust hasn't gotten too bad; it can be scrubbed off with a wire brush).

She was told "apparently, this is a normal thing for that car". Is this true? Do 70' Camaros have this problem?

yep and better check under the floor mats/rugs. and along the front and back window trim. :)