I dunno that you have to obsess over it and track every last AMP.
I prefer to go for big concepts:
1) A 30 amp trailer can be limiting and you can trip the breaker with relatively little effort.
2) Air conditioners pull a lot of amps.
3) Stuff that uses electricity to make heat pulls a lot of Amps. Electric space heater, microwave, hair drier, coffee pot.
(Gas furnaces and gas water heaters get their heat from the gas- not the electricity, thus they are not a big current draw*).
4) Don't run two big things at the same time if you are not willing to run out and flip the breaker back on...
4a) I'm not saying "never run two big draws at once"...you can indeed track the wattage/amp needs and run two things (the right things) at a time...but if it's the wrong two things- the breaker is likely to trip.
*"Big draw" is a relative term- When plugged in to electric hook ups- the furnace electricity use is minimal compared to 30 amps of never-ending power. When running off of a battery- the battery isn't "never ending", and the electrical draw (from the fan) does add up pretty quickly and can exhaust a battery in a day fairly easily.