Leaking AC unit

I have a 2010 330 Sundancer with a CruiseAir unit under the V berth. The AC unit sits overtop a drip/drain pan which drains to the shower sump. This drip/drain pan sits atop of a basin that does not have a drain. As the AC unit cools the cabin, this basin fills up with dripping water over the drip pan and can accumulate to pour over to the dry storage basins in the floor. It has been looked at by my mechanic at least 3 times and he cant seem to locate the issue. The drain line has been verified to be clean and open.

Any ideas?

If the drain line is open this would not occur.

Is the bilge sump box where the drain line is going to working?

Is it full so intern not allowing the water to exit the AC pan?