air box leak

have many water leaks on van - one makes small trickles a couple areas coming from the air box handler for the heater - in the passenger area - i dont have a heater assm or the piece to the right - so when it rains some water comes in air vent grill down into the air handler -the leak is where the air handler meets the front body -  now some does make it to the drain which the previous owner does not have a hose exiting outside -   and i take it this part is not removable - any ideas how to seal - its not like you can really get up inside of there -this was all not a big deal for previous owner - van came from utah - but here in the deep south i really need to start addressing these leaks -  oo3