arborsurgeon
None, just so as you have good insurance.

positive i
All you need to do is place your hand on the ceiling (over the flame). If it gets HOT, do not burn it. If it gets warm--just barely, then I would say it was safe. Do not burn it, though if it gets hot enough for you to pull your hand away, even after a minute. Your hand will not ignite as fast as a house would, so if you think there is any chance of fire, don't burn the candle!

DT
Not a good idea to burn a candle in a trailer. Get a battery lantern.

sensible_man
I wouldn't burn a candle near any walls or ceiling in a trailer. If you have ever seen a trailer burn, it is fast and furious.

stuckeymusic
positive i kind of has it. That works fine in a house, and you want to move it at least a couple of inches beyond the point that there is no heat transfer. The only problem is that in a trailer, your construction materials are different than in a house. If you have sheetrock in a trailer, it's only 1/4 inch thick. Panelling is usually thinner than that. They catch on fire MUCH quicker than those in a house, and they spread faster. It's horrible to say, but we used to joke around when my brother lived in a trailer that if it ever caught on fire he better be sitting right next to it or he could kiss his trailer goodbye. A majority of the time, a candle that catches a trailer on fire causes a total loss because the fire spreads so quickly. Because of this, I would never have a wall mounted candle holder in a trailer. Depending on what you are doing, it's probably not the ceiling you need to worry about as much as the wall it's mounted too. You need a minumum of 12 inches clearance for a small tea-light style candle to even be remotely safe in a trailer. More for a bigger candle that burns longer. Remember, burning longer means more heat output, which means more heat transfer to materials like what it's sitting on and what it's around. I have candles, so I'm definitely not anti-candle or anything, but I will tell you that you have to be really careful with them. One of the leading causes of residential fires is a candle. Many times it is too close to a curtain or other cloth material like a sofa and it catches the cloth on fire, then the next thing you know the Red Cross is finding you temporary housing. Be careful.

Dita
I'm not "anti candle". love them. But they can cause fire. Never leave a candle unattended even for a second. Never leave a child in charge of candles. Always have a means to put fire out nearby such as fire extinguisher. Inside the home I am right there, the candles are away from the wall and in a "pond" floating in a bowl. Not only safer but looks very cool. Consider candles or lanterns outside, I fill a low, shallow clay planter with clean sand, place the candle in it. Nice light for the patio or BBQ outside.