OP, by double door I'll assume you mean one with four doors... a Nocool 12xx which is 12 cu ft in size. They are a poor design without enough cooling coils in the back so proper air flow is very important and NO they do not cool as well as one with single top and bottom doors. In a slide where you do not have a roof vent you do not get thermal syphoning so extra fans are needed to increase the air flow. A 1200 comes with two fans and in a slide two more are usually needed. The proper rear spacing (air gap) is important and in a slide if there is a dead air space above the top vent (some have now gone to 4 vents) it disrupts the air flow.
I beleive the 1200s are more fire prone because they operate at higher temps than smaller units. Many of us have replaced our 1200 cooling units with Amish ones that have more coiling coils and thicker tubing so they are less likely to rupture and cause a fire.
OP, your friend needs to find someplace that can add extra fans and make sure it has the proper air flow, especially if in a slide before deciding to replace it.