a simple voltage check inside the trailer can tell u a lot. there is also a circuit tester that plugs into one of the outlets inside the trailer that can tell you if something is disconnected. (they cost abt $3 and look like one of those old adapters that use to adapt a 2 prong (no round ground) to a 3 prong appliance only it has 3 lights on it) only abt 3x longer. you should be able to find one at a lumber yard or good hardware store.
keep in mind, there are two grounds coming into the trailer. one is called neutral and the other ground. they origionate a the same bus in ur home and terminate at the same bus in the trailer. assuming you are going into a 3 prong service at ur home, even if u are adapting to a 2 hot in the trailer (50 amp) and you are wired at ur home correctly, u should have two grounds. the circuit tester will find if any one of the wires is open or connected wrong. you said that u have checked the connections and they are good. one of the comments above was to feel for hot (temperature wise) connections. if you have that, something is still loose. if all checks good, put a load on it and see if it is still good.
oh, also check the outlet that ur pluging into at home. u want to make sure it is correct. (use the little tester discribed above).
i'm assuming that u have this problem away from home as well as at home.
if u check all the connections and there is nothing wrong...even where u plug ur trailer in. then go back to a systematic approach to isolate the problem. if u turn the breakers on one by one and the problem happens on the last one u turned on. trip them all and start with the one that caused the problem. if it happens again, u've isolated the problem to that circuit. if it doesn't ur problem is at the trailer breaker box or before...ie ground or hot wire.
keep in mind, the writers above may have experienced this problem and found what they are telling u is the problem. in my case, i'm still trying to find the problem. there have been a number of post in forems that tell abt connections becoming loose in the breaker box due to either vibration or just not being tightened in the first place. with the power off (unpluged from outside source), check to make sure all of the connections between ur (supply) cable and the breaker box itself are tight.
whatever u find, let us know so we can check that if we get a similar problem.