@fanfare - shouldn't the OP check Box C? Box D is for lumpy withholdings (not estimates) and Box C is for lumpy income (which is what the OP stated).
https://www.irs.gov/pub/irs-pdf/f2210.pdf
Agree the form is a headache, but in this case it would be appropriate to complete.
@ArchesNationalPark - as long as you pay 90% of THIS YEARS liability by January 15 (since you are doing the RMD in December) AND complete Form 2210 (some of it will pre-populate by TT) you should be fine and avoid any interest penalties. The safe harbor is the LOWER of 100% of last year or 90% of this year.
