Hi.I have a huuuge map with many viewports (about 50). Is there any way to see the viewport-frames in the model, like a shaded rectangle, or suchlike?

Possibly.  Draw a polyline rectangle over one of your viewports.  Now use the CHSPACE command to move it to model space.  What happens?I could foresee some problems with what you are attempting to do.

I've done that Before, but it takes such time. I wondered if there was some automatic command or such

No, there is no magic automatic command that will do what you want.