Front leak while driving in the rain!

I just drove home from Florida to SC in the rain yesterday and arrived with a small creek flowing through my 1975 Tradewind! It is seeping from beneath the inner skin at the floor pretty much all across the front. Where is the best place to start to look for this leak, and how? It does not leak when parked in the rain so I am thinking that it is being pushed into the camper from how it flows while driving. I have never removed the inner skin, how hard is it to get back how it belongs when pulled out? Thanks for any help!