Alan, There are several manufacturers of keyless entry locks for houses. Both touchpad and pod. There are also a few that run off of a battery (triple A and 9 volt).
They are dead bolt by design.
The biggest issue installing one on a trailer door would be the thickness of the door. Mobile home door locksets are specifaclly designed for thinner doors, Depending on the lock design, you could probably modify the lockset to fit your door.
If the batteries fail, there is still a key you can use to gain entry. I have touchpad locks on my house that are powered by two triple AA batteries. They last about 6 months but give plenty of warning when they need to be replaced.
Pretty cool idea putting them on your trailer.