I eventually was able to resolve this issue by digging into the Camera Stacking thread ( Camera stacking for URP page-3#post-6278039). What I ended up doing is quite a bit simpler.
baseCam.targetTexture = screenRenderTexture;
uiCam.targetTexture = screenRenderTexture;
uiCam.Render(); // not sure why this is necessary but the first render will not render the UI
baseCam.Render(); // Will render both the base and overlay cameras
Just in case someone else is running into problems.