Install using gem 'savant-hosting', :github => 'savant-code/savant-hosting', :branch => 'master'.
Then ensure your routes.rb looks like this:
require 'savant-hosting'
Rails.application.routes.draw do
mount SavantHosting::Engine, at: '/'
end
You'll need to setup Devise on the host app as well:
Add gem "devise" to your Gemfile.
Run bundle exec rails g devise User in your wrapper app's directory.
Finally, the application.html.erb can be emptied and replace with: <%= render 'shared/application' %>