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It's a common practice, both in houses and TT to put a GFCI receptacle in and then "daisy chain" more receptacles downstream of the one GFCI, thus the downstream one are protected also. There may or may not be another GFCI receptacle in your trailer, it just depends on how it was wired. The reason that the GFCI was tripped is most likely there is an outside receptacle that is being fed from the GGCI and it got some moisture/water in it when the heavy rain started. I had the same thing happen a couple of weeks ago while at the track and we go a downpour that resembled a cow peeing on a flat rock. The GFCI recept. tripped, which killed the power to an outside recpt., a recpt in the bedroom, and maybe a couple of other. You might want to check the outside recpt. and make sure that the weatherproof cover is fully closed and that the caulk job around the cover is not letting any water/moisture into the recpt. area.