yes, it sounds like your recent trip you overloaded the 30a shore power breaker... demanding too much power all at the same time... while each of these items are fine to run on their own, several at the same time would push the power maximum.
sometimes the water heater might be ON, but not really creating heat, which is fine, but when it heats up the element, then it is drawing 10 to 15amps of power - if the AC is on at the same time, and then you run the microwave, you can see that the total requirement might be over 30amps.
of course, we many times forget about other 'fantom' power draws, such as a computer plugged in and charging, phone and tablet devices charging, lights, Fans, TVs on, Satellite receivers ON, and the coach's own battery Charger in process, etc.... you get the picture.
Usually the heat of the summer(running the AC) is the main time for power issues like this since it is the primary culprit when tripping breakers. If you have propane options, such as the propane water heater, or the propane fridge, then you can certainly keep those on propane and have much more power for everything else...
if you have an Inverter/Charger panel, you may also have a 'SHORE MAX' button or setting that you can modify when parked and on shore power. If you lower it to 5a or 10a instead of 20 or 30, the Charger will then use only that lower amount of amperage to maintain/charge the batteries, leaving much more for everything else. The only real reason to have it at a higher setting is if you really NEED the batteries to be charged quickly, such as when off-grid using the Generator... but under normal circumstances, even at 5amps, the batteries can be recharged during an overnight stay while on 30a shore power.
'14 Palazzo 33.3 bunkhouse 34' diesel
KingTailgater2 Dish HD, 100w/5a SOLAR, BlueOx
110,000+mi since '14 - US, Alaska, Canada (also, '14 Gulfstream Amerilite and '07 ForestRiver Rockwood) : )b