To work with the MC4 connectors, which are great and snap together, you (I) will need Y connectors every time you want to splice another panel into the mix. Since I have 3 panels, I found the perfect 3-Way Y connector on Amazon:
One connector is male-to-3-female, the other is female-to-3-male. Ahem. You need one of each because each panel has a positive (male) and negative connector coming out of it. So each panel plugs one wire into each of these 3-way connectors, and you have one pair coming out (the 1-side of each Y). Easy as cake.
A couple of extensions (15') and a special MC4-to-bare-wire pigtail and you can hook the panels up to the charge controller, which basically keeps the voltage and current under control so it's less flaky when it interacts with the rest of the system. The extensions go through a hole cut in the side of the trailer (gulp) with a Blue Sea Systems Side Entry CableClam (which I never knew existed, but is clever for waterproofing a through hole for a cable with connectors on the ends) to make it waterproof.