I have towed many things with many different tow vehicles.
From experience I will agree with everyone here. The lower the gears the better and the more displacement the engine the better. Now for something that i dont think anyone mentioned, "STOPPING" it one thing to get a load going but a whole different story on the stopping. This is were tow vehicle weight comes into play. Granted most travel trailers have electric breaks but having a heavier vehicle just adds to the overall control.
Things ive towed and with what; and some of these will be crazy
16' & 18 run-a-bout ski boats with mazda p/u 2.0L ok for short runs but wouldnt want to go long distances
jet ski with 5.0L thunderbird, no problems other than the independant rear suspention making it feel weird.
2 horse trailer loaded with jeep cj7, ok the jeep was modified with auto trans and 350 chevy but this is not something i ever want to do again. Even with trailer breaks it wasnt going to stop.
loaded 16' car hauler extimated weight 6500lbs with dodge 1500
5.2L the truck had a towing package and was rated for 8100lbs but wouldnt get out of its own way here.
28' enclosed race trailer with f-250 powerstroke, no problems here or with the 29' airstream, trailer brakes are nice here but didnt have them on the airstream first time I towed it yet it stopped well.
Thats just my penny but stopping is more important than getting started. My flight instructor once said take-offs are optional but landing are manditory.