Originally the scamps had a modified window air conditioner mounted in the bottom of a closet on the side. It was actually a pretty small unit, but you should not need much. I replaced mine with one that was about as small as you can get and it still will freeze you out quickly in very hot weather.
Now I would wonder if you had a leak or if the condensation from the air conditioner was the problem. That is a problem when one is done where it is mostly inside the condensation drains out of the bottom a lot of times and onto the floor.
now the way scamp
used to do this is like mine. Here are a couple pictures of what I have now. I replaced the old one when it failed. The unit is those grills right to the left of the door and it is in my closet where you hang clothing. Would probably have gotten one that mounts on top if the unit was built for that, but it was not and I didn't want to figure out how to make that work.
Now this is a several day job for a good handyman. And it takes time to find the right unit. It does have to fit. This is the about smallest you can get, but it also is a lot more powerful than the unit that was in there. The way it works is to kind of move the outside into the trailer. See the two grills to the side of the door. The took about 4 inch grill is an air inlet and it goes to the back of the part of the air conditioner that is normally outside. Or basically it comes into the middle of the air conditioner. Then the air conditioner does its magic and shots hotter air that then allows it to make cooler air for the inside straight out the back. That is the bottom section of the grill you are looking at.
You have to design and build a structure that will take travel into the closet to hold the air conditioner. And then you have to rig it so that the air can come in the top and then shoot out the back into the outside without the air mixing. The way I did that was to build a treated wood frame around the back that goes directly to the grill that exits the camper. You can actually get the grills at a home improvement store. Then you have to isolate the air flow of the outside air going through the unit from the inside. And it has to not leak and then has to accept that some water will come in the grills. Not as much as you would think, but some. and water is your enemy.
Then when you do all of that you also have to deal with the condensation I just mentioned. Normally air conditioners assume that most of them are outside and that they can drip water anywhere they want to except inside and right around the inside part. And that is bad. So you have to cut a hole in the bottom and then thread it and add a pipe to hose fitting in the bottom just enough to be full into the bottom where the water will be collecting. Then you have to run a short hose, and keep it short out the bottom of the unit. Then all of this needs to be sealed.
This is not a project for the newbee or the faint of heart. But it can be done. Mine is going on four years now.