I know this is an old thread (and JANETT and harveyrv haven't logged in since mid 2013), but there are not many threads on this subject and with all due respect to some who have already posted, I wanted to share some concerns I have. However, I'm no expert on this subject.
If there is damage to a section of the soft copper propane gas tubing under the trailer, I would recommend replacing the entire line. If one wants to splice the damaged section using a non-permanent/mechanical connection, I would not recommend using compression fittings because the road vibrations can eventually cause a gas leak with this type of fitting (compression fitting don't like vibrations, especially on soft copper. And it's usually not recommended to even use compression fittings in gas applications). Instead I would use flare fittings (requires special tools) for a better seal. Unless I'm mistaken, the factory installed tee fittings under trailer are the flare type. Here is a good video about flaring soft copper tubing:
Here is a good article about working with copper tubing:
http://www.g-w.com/pdf/sampchap/9781566379656_ch03.pdf
If there are any doubts about one's ability to safely repair any part of the propane system, hire a professional please or you may get burned.