Portable ac

I have a 12000 btu portable I use in my cabin and it works great,will freeze you out on a hot day. I know a lot of folks on here have tried them and they didnt seem to perform well .
Ya'll have me wondering why, do you think the trailers are so tight that they dont let it work well ,maybe opening a vent would make a difference. Most folks vent through the floor, hot air goes up not down ,I wonder if that could be the difference .
There has to be a reason they dont work in a trailer but do in a house.
Any Ideals or opinions?
Ron
Ya'll have me wondering why, do you think the trailers are so tight that they dont let it work well ,maybe opening a vent would make a difference. Most folks vent through the floor, hot air goes up not down ,I wonder if that could be the difference .
There has to be a reason they dont work in a trailer but do in a house.
Any Ideals or opinions?
Ron