I don't think it is smart to use tor as a proxy (e.g. 9050 or whatever) on a regular system. It is too easy for things to bypass tor (e.g. DNS lookups). Therefore I recommend doing it under whonix. In that case, everything goes over tor. Very few relays are .onion sites but tor has exit nodes so it should work fine. Gossip doesn't have any tor-specific code. You just run it from behind tor same as you run any other program behind tor.