Window shakers are sometimes misunderstood in their design so I am not surprised when I see some of the creative installs on FBRV.
Usually I make no comment unless asked a questions directly as people show great pride and effort into the issues installing their window A/Cs, not wanting to steal thunder I am often aware how the install may function regardless of the pride in its looks.
To answer the question first you pose...
Water is generally disposed of in window units with the use of a slinger ring attached to the outside circumference of the outside condenser fan, the water exits the evaporator (the inside coil you see)
at the bottom of that coil, in a tray made of Styrofoam usually and has channels molded into it. These channels allow water to trickle out of the inside area to the outside area without mixing the air moving inside or outside, the slinger ring outside is spinning being attached to the fan blade (a big circle)
dipping into that water throwing "slings"
it as it picks it up a tiny bit at a time, this aspirates it against the hot outside coil, this increases the efficiency of the outside condenser coil boiling off the water so to speak.
In humid climes where there is allot of water entering the system from the cold coil condensing it out of the humid air problems occur. The condenser cannot burn it off fast enough sometimes so an over flow is employed. This excess water drips off a notch at the rear of the a/c or in some units a tube is used...This is no longer done in current designs favoring the notch at the rear today.
In some A/C installs I have witnessed as of late the owners do not want to put the back of the unit outside the trailer as it disturbs the looks of their eggs...The unit is designed to hang out so outside ambient hot air blows thru its outside coils only,
while cool inside air blows thru the inside coil only
and the two NEVER
mix...They are separate operating systems on purpose. When this rule is changed in the manner of its install issues will present themselves not thought of.
air is purposed to the outside
coil water cannot evaporate fast enough, on a 100 degree day with 100% humidity the coil using inside air for the outside coil will hit 110 degrees about, not 140 degrees as it was designed for, it needs the hotter air supply. The tilt of this unit must also be about 3 degrees to the rear outside coil or water will flow everywhere. Never must it tilt towards the inside coil.
When these window shakers are used in closets for instance great care must be given to the tilt and the absolute need to use outside air for the outside coil, and inside air for the inside coil.
I hope this helps, your specific cure
is a unique
situation to your trailer install and I am not aware of its install or model, also how what air is dedicated to its parts of operation is done in your case. If inside air flows thru the outside coil for instance the water is re-evaporating into the trailer over and over until the inside coil is overwhelmed and it goes everywhere.
If I could have a peek at your install it would help my answer to be more specific to your install.
A drain system is always a good idea, sealing it into the pan is a must.
The reason water is eliminated
is the capacity to cool is greatly diminished when air is moist, also physics requires that to occur first BEFORE
the temperature of air drops even one degree.
It works like this, if in one square cubic foot of dry air we remove 1 b.t.u. (measure of heat) that air will drop 1 degree. We moistion that same cubic foot of air and we will need to remove 144 b.t.u.s of heat to create water, then when the water is extracted the air may drop 1 degree.
This is why A/C units must be managed in certain ways, physics is the task master in design.
For those who want to box the A/C unit behind secret unseen places must place great thought to separate ducted air supplies (for the outside air)
for these units...think inside/outside air always.
Happy Camping, Safe trails.