Cute little radio. External antennas (mounted as high and as clear as possible) are almost always better than the "rubber duckies"

You want an antenna that's tuned for the frequency of interest. In this case, VHF air band. You can surely buy a mast-mount aviation antenna thru any number of aviation supply houses. Question is what kind of antenna connector is on the radio vs. what comes with the antenna. You also have to consider the losses in any cable to the antenna. But generally you'll hear a lot more with a proper 1/4 wave antenna in the attic thru 20' of coax than you will using the rubber antenna. If the antenna is up 100' on a mast - so much the better.