It's sad but the industry's NEMA TT30R/P design is really under engineered IMHO. Many decades ago when it was created, there were no electric water heaters (in RV's) or micros, TV's, large battery chargers, etc. Just some lights and the occasional space heater. Then add in poor quality, off shore parts and it only gets worse.
We use a lot more of the capacity if these "trailer" circuits now and while they work OK when everything is perfect, they don't like running a constant load at anywhere close to their 30A rating.
It's too bad we can't switch over to the marine undustrys 30A receptacle for pedestals. It seems to hold up better.