Another great alternative in this space is dokku[0]. Haven't tried CapRover recently but it looks fantastic.
Migrating the docker image building from the dokku server to a CI would be easier to do without this. On top of that, deploying an existing software into your machine would be easier.
[1] http://dokku.viewdocs.io/dokku/deployment/methods/images/#de...
So basically, you could put a Dockerfile file container just FROM and MAINTAINER, referring the image you want to use in the FROM, and dokku will download and execute it on `git push` (provided it can access to the image repository).
I wonder if there's a ticket about this on dokku already
[EDIT] - Couldn't find anything... Some tickets about how the containers are built and changing the base image but not much about.
I wonder if you could jury rig something like kraken[0] and make sure wherever your building images is a peer or something... Of course the simpler solution might be to add a CI step that just pushes the image (via the working `docker save` method) to the deployment machine(s)? Maybe if you have a staging environment, let CI push there, then if that machine is peered (via something like kraken) with production, production will get the image (though it may never run the image).