So I have an 88 Rx but this applies to any who have a coupe.

 

Right behind the doors on both sides there are holes in the body that the trim disguise. 

What are they for? I don't have any trim so I am thinking of welding them closed.

Not sure what they would be for.  BUT if you can't get rustproofing / paint on the inside after welding, that's a problem...

The vents are there to keep the cabin pressure from getting too high on hot days, which can result in busted windows.

So there must be drain holes for water too right? I was thinking there must be if its open to the outside. 

The passage is usually designed to route up into the cabin in a way that water can't get in. I can't say specifically to the ea82 3 doors. But that's how it is on the ea81 cars. Your brat has the same type vent hidden behind the side trim behind the door windows.

There'll be a rubber flap on the inside that hangs from the top.

It's not just there for hot days, it also allows the air pressure in your car somewhere to escape to when you close the doors.

 

Now I'm trying to remember where they are for the sedan & wagon...

More modern cars tend to hide them behind the rear bumper as there's more plastic there without externally visible metal.

On my coupe I don't have anything to keep water from entering. So even with the trim in place, water can still enter, so there must be weep holes somewhere. 

You can see in that it goes nowhere but into the cavity. I don't believe she is missing anything. I got the car from someone who didn't do anything to the car and wouldn't know otherwise. 

Edited March 20, 20179 yr by Naked Buell

It's for more than venting on hot days, it's a critical part of the HVAC system. Think about it, if you have the heater fan on high trying to defrost the windows, and it's pulling air from outside, where's it going to blow the air out of if all the windows are shut? You need a place for air to get out of the car if it's getting blown in by the fan. That's what those are there for.

 

The rocker panels have multiple drain slots in the pinch weld area. That lets any water that gets in drain out.