Thor Palazzo 33.3 diesel
Brand: Thor Motor Coach
Model: Palazzo 33.3 34'bunkhouse
While I'm not sure what brand/number/size your inverter is, I will assume it is a Magnum ME2012 or similar MS2012, like mine, in our 50amp Palazzo. The inverter receives CHARGING during Shore Power hookup, or Generator runs. The inverter produces 120v output, from the batteries, ONLY when it is actually inverting, while off-grid with NO shore power or generator. The Inverter will only be 'passing thru' 120v power when you are plugged in or on the generator - only how 'much' 120v will be tempered by the number and size of your individual breakers and main breaker for your Inverter sub-panel, which is either a separate panel, or integrated into your main Electric panel, like mine.
If the breaker that serves your Inverter's CHARGER, is 30amp, like mine, you'll only have access to 30amps of 120v power to all of your individual breakers powered by the inverter. If you have two HEATERS plugged in and running, and you are powering TVs and satellites receivers, and the FRIDGE, and other 120v items, then you can easily TRIP one of these breakers, or the MAIN inverter breaker(30amp), if trying to do too many 'things' at once, EVEN when on 50amp(100amp) Shore Power. The Microwave, StoveTop, and any other high-draw items, which plug into a 120v outlet, are ALSO run thru the inverter breakers/Main breaker.
You may have an individual breaker for the microwave, one for the stovetop, one for the GFCI circuit outlets, and another for the other 'regular' outlets, for TVs and general usage.
You SYMPTOMS, though, are not indicative of the normal actions for how these systems are supposed to work.
In your explanation, I suppose that you are saying that only WHEN you use the microwave or the stovetop you are experiencing these 'brown out' situations, in conjunction of the usage of the two heaters at the same time. Heaters draw a LARGE amount of amps, especially when on HIGH, sometimes up to 12-15amps each on their own. The other items such as TVs will not draw much amperage, and the FRIDGE will only be drawing amps during it's compressor runs, generally every 10-15mins or so, for about the same amount of time.
So, when you add another large draw, like the microwave or the stovetop, you may experience TRIPPING of an individual breaker for THAT specific circuit, IF the microwave or stovetop is SHARING that circuit with other items, such as the heaters. If these two items have their OWN circuit breakers, then you may experience the Inverter's MAIN breaker trip, or the same if several individual breakers exceed the 30amps of the Main breaker between them.
All-in-all, though, your INVERTER should not be in play, as for the 'inverting', during your use of SHORE POWER, as it is only passing thru power from the shore/AutoTransferSwitch(or generator). If you exceed the 30amps for the inverter's Main breaker, it should trip, or the Inverter's OWN 30amp push-breaker should trip, as you are asking it to 'pass thru' more power than it is capable of.
But, in any case, this should have NOTHING to do with you Inverter 'losing power' because the inverter is not working, it is only passing thru power. No 'brown out' should be occurring, not even to your 12v items like your lights, fans, water pump, furnace, etc., since they run directly from the batteries.
My diagnosis is that you may have only one SIDE of your 50amp service that is LIVE from the shore power. Either your Shore cord has a loose hot wire, or your ATS(automatic transfer switch) has a loose wire, or the Shore Power's own double-pole breaker has a loose wire on one of it's breaker sides.
You would have 50amps of 120v power to much of your coach, maybe the side that feeds the Inverter's CHARGER, AND therefore the Heaters you have plugged in, as WELL as the Microwave and/or stove top. So, everything works pretty much as you expect, but when the overload occurs, you have then lost ALL power to the coach, and the Inverter then automatically takes over, which it is designed to do if you have it 'ON' and ready. The heaters, though, because of their LARGE loads, and the addition of the microwave or stovetop, are now DRAWING DOWN THE BATTERIES IMMEDIATELY to a critical point, when you experience fluctuations and flickering of all 12v items, such as lights, and eventually lose the Inverter as well, with all 120v items being lost.
ONE THING TO TRY: use your generator, and see if the same conditions occur - if they continue to work as they should, while on the generator, then you have simply lost power on one side of your SHore POwer.
and a note: while it 'could' be low campground power, such that you are not consistently receiving 120v power, especially if it falls below an acceptable number, such as 105v, generally your coach would continue to 'work', but you may see that the heaters, microwave, and stovetop don't work as efficiently and as powerfully as when on full 120v power. It 'could' also cause a rise in amperage due to the low voltage, but that would still cause tripping of breakers, not a 'brown out', or similar explanation, or generally cause the inverter to take over.
'14 Palazzo 33.3 bunkhouse 34' diesel
KingTailgater2 Dish HD, 100w/5a SOLAR, BlueOx
100,000+mi since '14 - US, Alaska, Canada - Hiawassee, GA! (also, '14 Gulfstream Amerilite and '07 ForestRiver Rockwood) : )