Your going to haft to help us out a little to find out what is wrong.
I take you have read the posts in this thread already.

How long does it run before it dies?
When it dies will it start right back up or do you half to wait a while.
If it does not start right back up can you hear the frame fuel pump run for one second each time you turn on the key?
Dose this RV have a Fuel Injected engine?