I have a champ 3400 inverter model
I would wait they the winter and see how the reviews, reports, and any complaints, play out
Then decide
Yes altitude will affect the generator
It will cause a power reduction, and you have to be more power aware when switching items on and off , keep the fridge and water heater on lp manually all the time,
Maybe do some charge time generator running , BEFORE you make coffee, use the microwave or A/C, or hair dryer
Maybe turn off converter first, do breakfast, then turn on converter for battery charging,
Carry some starter fluid just in case , you run into a hard start situation
Any low altitude gas you are carrying, will evaporate faster
And make for hard starting , is the T/V diesel or gas, buy fuel on the way up the mountain, not down in the low land