FIG. 1 is a right perspective view of a freestanding gas fireplace cabinet embodying our new and ornamental design;

FIG. 2 is a front elevation thereof;

FIG. 3 is a right side elevation thereof;

FIG. 4 is a rear elevation thereof;

FIG. 5 is a left side elevation thereof;

FIG. 6 is a top plan view thereof; and,

FIG. 7 is a bottom plan view thereof.

The cross hatching in FIGS. 1-3 and 5 represents screening and is understood to entend uniformly throughout the area represented. The broken line showing of environmental structure in FIGS. 4 and 7 is for illustrative purposes only and forms no part of the claimed design.