You can pop the top up and add water with a hose along
the bottom boot to find if it is leaking. Just do a short section
at a time...maybe even work your way up from the bottom of the van
to test the windows, exterior light and anything bolted to
the body. My awning supports leaked once but caught it quickly
before stuff went bad. I also had the wire loom of the solar
become a conduit for water. At the same time, water entered
the top and ran to the overhead lights. I drove around a corner
and water rushed out of the light
There is a big write up
on the PH top bolts leaking that Jage did but I'll bet the water
is coming in elsewhere. I'd take a real close look at the butyl
seal at the base of the PH. Good luck and post what you find.