I have a detail list on the repairs line for all of my Sch E properties, something to the effect:

Safe Harbor for Small Taxpayers:
Lesser of $10,000 or 2% of $xxx,xxx [using actual number for property] = $x,xxx.

Then I list the details underneath w/date, description, amount.

I also put in a reminder if I need to flip the election in the following year.  i.e. if 2019 has an $8K improvement vs. $4K 2% limit, I have to turn off the safe harbor election for 2019 and remember to turn it back on for 2020.

The good news, it is property by property so just because you fail on one property you can still use it on the others.

Rick