I am also getting the LoadError: cannot load such file -- rubber
The Capfile is looking for the dependency rubber, which it cannot find.
Apparently my Gemfile has not been changed during vulcanize.

I should add that I originally created my project with rails composer, which added capistrano to it. During the bundle command, I gave permission to override all files, for whose it prompted me. This should have undone all rails composer magic.

I had to add:

gem 'rubber', '~>3.1.0'
gem 'open4'
gem 'gelf'
gem 'graylog2_exceptions', :git => 'git://github.com/wr0ngway/graylog2_exceptions.git'
gem 'graylog2-resque'

and

group :development do
 ...
  gem 'capistrano', "~> 2.15.7"
end

You may have to run bundle or bundle update depending upon gem's present on your machine.

TIP: if you are planning on testing rubber, I would suggest destroying instances

cap rubber:destroy

after you have tested it. Or find a free tier ami

 region: ap-southeast-1
 image_type: t1.micro #free tier
 image_id: ami-a4ca8df6

So that you don't have to pay hefty bills :).

Hope that helps!

Cheers,
Jeremy