Thought I would get some opinions on this, for a while I have been aware that the battery tray area of my 91 190e (not my daily) was super corroded. As for the wheel well, it is mostly rust free except a small hole and surface rust. Fortunately because the car was been mostly covered/protected it has not spread excessively. I am in the process of preparing to remove the rust out, and have someone weld in patches for me (reputable guy, runs a small local body shop fair price and has done work for some friends in the past.) Luckily I have experience with rust, and I have a complete 92 parts car that will provide patch panels for me. My question is about how the area under/around the battery is supposed to drain. I have not replaced the seal on the right side (air inlet cowl to hood), but I have determined that the drain in that area is clogged, so it is on my agenda to clear out. Aside from that I have noticed a hole (looks like a factory cavity it is not corroded), and recently lined the area with some baggies before a rainstorm. The result was a considerable amount of water ended up in the bags. I have tried looking at xentry, manuals, and pictures of other 190e’s but am unable to determine what is causing the poor draining of the battery area. I would like to have this figured out before getting the area repaired, any insight would be appreciated.

I don't know what that cars battery area look like but most older cars have no special drainage. Generally there should be no leakage, or no significant leakage. The only time I see it when using the wrong batt off-road, or over charging, or charging too fast. So with the latter two I see it a lot on trailers and RV's where people put a charger on high and leave it, or a really powerful charger on, but basically the harder you charge it the more bubbles it makes, and with bubbles you get some liquid. Once fully charged it makes even more bubbles, so having said that, a bad voltage reg can cause over charging.
Too much water in the batt can cause leakage too, which is what I do because I'd rather have a little leakage than dry plates, so I over fill, prob solved.
So in your case, if it were me, I'd just not worry about it unless you actually have an issue as described above. I mean it takes a long time for acid to damage the metal so do you expect the car to last so long it'll eat thru the repair job? If so, some options include a batt with a drain vent line, like my current oem MB batt has which vents all gas/liq to one port on the batt which has a plastic line to get it down and out of the car (on the ground). Or a sealed battery, and I mean a real one, like an Optimus that you can even run it upside down and it still won't leak (yes I've done this). Prob solved. Or buy a plastic battery box to put the batt in, you see them for boats, trailers etc. Or make one, or put the batt on a thick stack of paper towels, maybe sprinkle baking soda between the layers of paper. Fyi, for the trailers etc that often have issues I'll dissolve a good bit of baking soda in water, which I put in a spray bottle. Now I can spray the whole battery etc which both neutralizes the acid but also shows me where all it got to. Also handy when you realize you have some acid on you, or worse, some on your fingers and you rub your eye. It happens