Electrical shore power entry problem. Input cable shows 120v, but nothing inside.

Hey, folks, I've got a weird situation with our 2000 Keystone Monaco that's parked on our property. We've built a solar set up on the property in preparation for building our home there. Until it was completed, we would use a generator to power any AC, which wasn't on often, since the 5th wheel is mainly used as a tool crib and rain shelter for our work down there. A few weeks ago, when I got the solar up and running, I turned on the 30A breaker in the shed where the PV equipment is housed, which feeds a 30A, 10ga 100' extension cable to the 5'er. It didn't have a battery in it at the time, as I had pulled the old one to bring home and check it, but everything kicked on as it should (lights, AC and furnace fan, and I could hear the hum of the converter even though it had no battery connected). Yesterday, after doing some tweaking on the system's charge controllers, I once again flipped on the 30A breaker on the service panel beside the PV set up. Went over to the trailer and there was no power, except for the DC side (I installed a new Grenerer LiFePo 100A battery when I got there, so it was doing fine). I used my Fluke 117 multimeter and checked voltage at the socket mounted on the outside of the power shed, which is about a 5' line run from the service panel, and had 120v on one leg of that outlet. Then I checked the other end of the 100' line to the 5th wheel, and it showed 120v, also. But inside, there were no lights, no HVAC fan, no converter hum and no power at the 110 outlets. I then checked to see if all the breakers were closed, both in the "breaker box" at the door, and also the breaker at the rear wall where the power entrance is located outside of that spot. There's a 2 pole and a single pole there, and someone previously stuck a label 'water heater' there, although it's in the center of the two sets of switches, so I'm assuming the double pole is the water heater. Although we've never used the wh in the 4 years we've owned this 5th wheel, the whole trailer was gone over by a local rv sales and service shop and it was working then. Anyway, before I start removing and inspecting breakers in the trailer, I'm wondering if anyone here has heard of this happening, or maybe can tell me something I'm missing. Our PV (photovoltaic) system is 8kw of panels fed through two Midnite Solar Classic 150 charge controllers, two Trace SW5548 inverter/chargers and a rack of (5) SOK 100AH LiFePo batteries that are fully charged. 

Since the system did fine just a week or so ago, I'm not sure where the problem is. What would be the steps in the troubleshooting procedure for this? I'm sort of thinking it may be the breaker in that box under the rear window, which means I need to pull it out and test it. But if anyone has a suggestion, or hopefully, someone may have had this problem at some time, I would really appreciate hearing about it. I'm able to dismantle and check anything in the system (that's not buried in the walls or floor), but it's pretty nippy here in southeast Missouri this week, so I'm trying to be smart and get help from the experts, which would be all of you. Thanks in advance for any comments and ideas. Lee