You already can dig water moats in Life is feudal, so it would be great to build a Stone Gatehouse with a Drawbridge and a Castle Gatehouse with a Drawbridge - maybe a Palisade Gatehouse with a Drawbridge, too. ^^
And it should work like this:
You can lower and raise the Drawbridge from the Gatehouse with a Drawbridge just like open and close the current Gatehouse with the Portcullis and it should work in exactly the same way. When you open it, then it lowers down (so you can get in and out) and when you close it, then it raises up (and you can't get it and out).
The Drawbridge should be long enough to bridge the moat, so the Drawbridge from the Castle Gatehouse should be longer as the Drawbridge from the Stone Gatehouse (or the Palisade Gatehouse).