Scott;Welcome to LF Radio. I run the WM Lowfer Beacon, but it is currently off for the summer. I plan to fire it back up after the grass mowing season ends. Most likely by Mid October. I believe most other Lowfer transmitters are off for the summer.
I too have used the RTL-SDR devices over the years as LF receivers. I currently am using the RTL-SDR V4 device, which has the built in up-converter that covers the 0-30 MHZ freqs. I find that it works fairly well on my antennas, but it does have a couple LF issues that need attention.
May I suggest that you check out the "ndblist" on groups dot io. (I hope I don't run afoul of the forum rules by writing that link.) They run a Coordinated Listening Event every month, which can give you some practice getting your station going on LF, and maybe have a little fun to boot before we get the lowfers going this fall. In last months CLE I used both my KiwiSDR and V4 for an A/B comparison, and found the V4 only slightly less sensitive than the KiwiSDR.
Good Luck
Mike N8OOU 73
Again I welcome you to the Lowfer group, it is really nice to get a report from a new station/location.