There are very few things you can do and a whole lot of myths.
What can you do: Lower your profile.. Basically do not put up antennas
Do not plug in to shore power.
Try very hard to NOT be the tallest object nearby.. Example a 20 foot tree may well protect a 60' circle (Radius) but your roof has to be in the cone.. and the tree may hit you if it gets hit.
That's about it.
Myths:
I have heard folks yammer about not putting jacks down because they provide a ground path and the tires will insulate you.. Sure they will.. A ligntening bolt that just jumped thousands of feet is going to be stopped by say six inches of rubber tire..... Think about it. One of the funniest jokes I've ever heard.
You are safer inside the RV as the SHELL may protect you, epically if it's metal roof and sides.. A car (All metal) is good too, but only because of the protection (Which by the way is less than complete) offered by the metal shell.. Fiberglass bodies are not much protection.