Rain dripping down SS liner

Hi All- need some help. I have an insert with a Magnaflex stainless steel/Titanium liner. I have noticed that when it rains water drips down the liner. You can hear it dripping inside and it drips down into the back of the firebox. It is not a flood, but it can be enough to turn the ash in the firebox to mud. I spoke with my installer who said it is just due to rain blowing in when it is heavy and there are winds. It only seems to happen during heavier rains. Does this seem normal? Do others have this problem? Do you accept their explanation? Any solutions?

Thanks!

I will get a picture up when I get back from work today. There is a cap over the top, but maybe it needs a bigger one.