This is easy stuff, especially in vegas. You should have no problem keeping sync the whole time.
Easiest if you start both cams and let them run wthout stopping - just for changing tapes.
You should find that when you lay both tracks on the timeline in vegas, one below the other, you can line them up at one spot and they will remain in sync to the end.
You can do a rough alignment by video or just listening, but for the precise alignment use the AUDIO waveform. Expand the timeline maybe to the frame level so you can line up the audio waveforms by eye, easily. Should stay in sync from start to finish as long as both tapes roll the whole itme.