We had our trailer wrapped in the weeks just before CMP 2015. We had a team-internal "call for designs", but had a professional outfit (who happened to live next door to a team family) execute it.
It looks great! We keep it in the great outdoors, in the subtropical sun and rain of southeast Louisiana, and after a year and a half, it still looks like new. The plastic does not attract a whole lot of dirt, and our fairly frequent heavy showers are usually enough to keep it from getting very dirty, though I know we washed it at least once (this June or July) after a few weeks of dry weather. Not only does it look great going down the road, but it's a permanent recruiting billboard - nearly every student is at least aware that we have a robotics team. Definitely worth it - if you have a team trailer or vehicle, wrap it!
Apart from the Ingersoll Rand logo (and they paid for the trailer, so though we're obligated to advertise for three years, we'll leave it at least as long as the wrap lasts) and NASA (who we were confident would take us as a "house team," though they hadn't at that point), we put all of the sponsor logos on the much smaller front faces of the trailer. We added stickers for a couple of new sponsors, and plan to replace these faces in early 2017 when we have a better list of current sponsors. Based on conversations with some local business owners who have wrapped, we expect to do a complete re-wrap in another two to five more years (4-7 total) when the current wrap is no longer as nice looking as it is now. I fully expect that the durability of a wrap is dependent on local weather patterns.