Hmmm, we have on occasion (at least one time-that I can remember) gotten up to around 49A incoming, however, that is with 50A service which all know is really two legs of 120VAC @ 50A per leg. 30A is only 120VAC @ 30A on ONE hot leg. However, it seems to me, that the inverter should have kicked in, to provide the additional current needed to power the two devices, my coach does and has done it lots of times when we were plugged into 30A shore power. We never blew fuse or even tripped breaker. We have induction cooktop, was using one side of that, electric oasis heat both sides, and maybe I started a heat pump to take chill off the rear area. Anyway, nothing blew. Suggest you might take the time to ensure all electrical connections on both chassis and house battery banks are tight. I did that first after getting coach home from purchase. None were lose, but some were not as tight as I wanted, smeared NO-OX-ID-Special A all over them to keep corrosion down. And although situation has been remedied, still think it should not have happened, through inverter it should have been able to handle at least 60A and some of the total load was handled by the 30A SP. Since all receptacles are 15A max, except the microwave is a 20A dedicated circuit. If I remember correctly, mine (cooked chicken on convection) was using about 18A, the cooktop (substitute the air fryer) would use another maybe 13A, 31 total, the inverter should have kicked in. The fuse which blew, was on the DC side of the house, and as such would not have been carrying the complete load of the coach, because the 30A shore power would allow the inverter to "pass through) until it reached 30A and then kicking in providing the other amps needed, no where near the max as shown in another post. So something is not kosher in Denmark based on the explanation so far and the solutions outlined so far. Or, I am completely missing the facts. My guess is, the fuse was not a good manufacturer and/or had some corrosion internal which caused it to fail. Don't think they have date codes, but twas me, if they do, I would make sure I had one with a real current manufacturer date. I have only heard this happening less than 10 times, so this is a rare occurrence.
