If connected in series, the voltage is probably 90V to 180V. If one had a leakage path to frame, that could be a hazard.
If parallel, voltage is much lower (although Voc of a "24V" panel isn't something you should touch while wet.)
We normally wire the frames together and back to equipment chassis and a ground rod somewhere as part of our permanent installations. The RV guys with some portable panels don't.