Determining rms of AM carrier


I am interested in determining the rms strength of the carrier of an AM
modulated waveform, and displaying it in realtime, perhaps as a windowed
average value. I am using the LFRX boards on the USRP. This question
probably comes up a lot in the SNR and RSSI related posts, but perhaps
not specifically for my application. Are there currently tools
available in the gnuradio libs for this? If not, I would appreciate a
run-down of what technique is needed to do this, and if there are any
related codes that can be used as a guide. In principle it would seem
to me that just measuring the rms of the I or Q stream would be
sufficient if the modulation index is low (which it is). If not, then
perhaps dividing the I or Q stream with the modulation (obtained with