A/C leaking into teardrop

[eugenewright]

Hi all,
We have a teardrop with an A/C mounted on the back (the end where a galley would be if there were a galley). We have some trouble with rain getting in through the A/C and inside the teardrop. We have a small cover that we put on the A/C but it doesn't quite cover all of the vents. Anyone have any suggestions for a fix?
Thanks in advance!

[steve cowan]

A picture of the unit would help with advice for a remedy.Without that would a bigger cover work?