Hello Joe -- -- --
Using an inverter for the micro is like starting the tractor motor (well almost) As there is a current drain for a short period of time. This won't harm the batteries -- Which is your real concern.
Another example is -- you run the fridge over night -- and the converter draws appx 3-4 amps continous all night. Does this harm starting batteries ?? My answer is no -- although deep cycle batteries can standup to this demand better than starting batteries.
My view is -- does the end justify the means. And for me -- I'll replace the starting batteries every 5 years -- and install 4.
Hooking up an inverter -- By the way -- Full current is available at any of the 3 - batteries. But -- You'll want to only hookup to the Front battery. If you hookup to the rear battery -- you will be removing the nuts holding down the battery cables -- and you will loose power to the tractor. This causes no harm -- Except you'll have to reset all the clocks ........ :^) Thats why -- When you view my photo's I used the Front battery -- the end battery in the string -- and only one cable on the post -- plenty of room for another !!
Hope this has helped ........