Tilt your solar panels so they are not facing the direction of the hail. Specifically how to tilt your panels will depend on what hardware you used to mount the panels in the first place, but this step will most likely involve getting on the roof with an Allen wrench. Or, if it is easier, simply turn your RV in such a direction that the panels are facing away from the direction of the hail.
Drape a thick blanket over the panels (an old one you do not mind getting wet). Although this may sound like a low-tech solution, many professional electricians and solar installers use the "drape-a-blanket" technique to protect themselves from currents when working on a roof because draping a blanket over the panels also prevents them from generating electricity.
Throw a tarpaulin over your blanket to protect it from the rain. This will not protect the blanket from getting wet, but it should add another--and a thicker--protective layer and keep the blanket from getting immediately drenched and soggy.
Link one end of a bungee cord or ratchet strap to one side of your RV, toss it over the roof and cinch it down on the other side to hold your blanket in place.
Repeat, spacing each cord or strap a maximum of 6 feet apart, and ensure you have a cord or strap at each end and one in the middle. Repeat as often as necessary, depending on the size of your roof and number of panels.
