engine/app/uploaders/theme_uploader.rb

class ThemeUploader < ::CarrierWave::Uploader::Base

  def store_dir
    if Locomotive.config.delayed_job
      self.build_store_dir('sites', model.id.to_s, 'tmp', 'themes')
    else
      "#{Rails.root}/tmp/themes"
    end
  end

  def extension_white_list
    %w(zip)
  end

end