my 07 GT has an access panel under the rear seat for the fuel pump. I'd never do it to my Fox though. I've got all the tools and a lift to do it the right way.
I just did the rear struts on my dad's 1990 5 spd. corolla, the backseat had to come out to get to the top 3 strut bolts, right under the middle of the seat is the fuel tank, it also had a little metal plate held in 3 screws with a harness coming out of it to get to it. Looks like one of the ones posted above, I can post a pic if someone wants.
You want an aircraft style inspection cover with a reinforcing ring doubler.
Send me the dimensions of the hole and I will post a drawing of what you need.
It would be nice to have a picture with dimensions of the hole you cut.