When you start messing with the cover that is part of the way the condensate drains and needs to be put back like you found it or you might develop a leak Taking the top off is the easiest way IMO but you'll probably give the customer a heart attack when they see it apart
You must be thinking about the fan plenum which is below the evaporator coil on the True prep units. Yes, those are part of the condensate drainage and there's rarely a need to remove one of those...except I have seen a lot of them rotted out where the plenum seals to the bottom pan, creating some bad condensate leaks. Then I simply get them warm & dry and reseal with lots of silicon.
The exception is what I'm talking about the whole coil gets wet and in some cases the water tracks.
Where the two sections meet is a tiny lip the coil shroud sits into the lower fan shroud and the back and front need to be back to normal or headache.
I have just bend the top of the plenum lip over (without breaking any silicone and slide the coil up a bit (sits loose in the plenum) and hit it from the front easier but I still think its better to just pop the top so you don't need to pull shelves or outer cover with those crazy screws, scratching the interior paint up and bust your back in the process
Trust me will stink less when you're done this way too since your not sitting in all the muck