Sorry to hear of your problem.If the floor is wet under the van, but not yet inside, I would suspect water is finding its way past seals such as the front or other locker , roadlights, windows, awning rail or front gutter...
I would suggest use of a damp meter inside to try to trace the source.
On the outside, look for signs of splits or cracks in any visible mastic as this may be the cause.
If you have a gutter across the front window, try adding a short length of hose (say 9")to each end. This carries water away from the van which would otherwise run down the front body seams-its very effective.
Hope this helps a bit