I'm pretty cautious when it comes to weather, having spent more than a few nights in the basement when tornadoes swept through. I think if I was boondocking and had that forecast I would probably plan to get in the truck and find a hotel for the night. Depending on the size of the storm, I might leave the area with my TT in tow.
I am not a fan of braving a bad storm in an RV. Only once have I done it and in a pop-up, no less. Holy cow! that storm blew up in about 10 minutes and just pounded us. It was so bad we were afraid to leave the pop-up for fear of getting hit by lightning. When the storm cleared and we came out, there was a tree about 10 feet from the pop-up that was cleaved clean in half all the way to the root. Scared the******out of us. We have never tried to ride out a bad storm in our rig since then.