Camper Leaking

I have a problem with our Camper Trailer leaking through the roof.
I have read all of the forum threads on leaks but mine seems different.
I have had it up in a number of heavy downpours but it still leaks.
It's been up in the back yard for the past week and over the last two days we've had well over 200mm of rain.
I sponged it out today and there was a third of a bucket of water.
The strange thing is the only water coming in is dripping off the internal metal frame where it makes contact with the roof. There are vinyl protectors on the corners of the frame and no water appears to be dripping off them only off the metal. At times water has pooled on the roof but it hasn't leaked through in that area.
There are no seams across the roof so it's not a leaking seam.
I've put some vinyl over the exposed metal in one section and will wait for it to rain again to see if it still comes in in that area.
It looks like my options are either to waterproof the whole roof or use a fly.
Does anyone have any idea why this is happening and the best way to fix it.