One other possibility: if you're performing it through a sound system, lean right into the mic on the low notes and let its 'proximity' effect reinforce the bass.

(I attend some country jams and sometimes do the old Jim Reeves song "He'll Have to Go". To get the range I have to do it in 'D' and use that swallow-the-mic technique for the octave drop on the line "..jukebox way down *low*". Works.)