Rails n-level multi select categories

I have a rails 3.2 project in which I have Projects, Categories, and ProjectCategories.

A project:

has_many :project_categories
has_many :categories, through: :project_categories

A Category:

has_many :subcategories, class_name: 'Category', foreign_key: 'parent_category_id', dependent: :destroy
belongs_to :parent_category, class_name: 'Category'

has_many :project_categories, dependent: :destroy
has_many :projects, through: :project_categories

A ProjectCategory:

belongs_to :category
belongs_to :project

So a category has n-levels of nesting in it.

I am trying to create a form where the user selects 1 or more top level categories for a project. Based on these selections, the user sees their children categories and can select 1 or more of these. This is repeated until there are no more child levels.

All of these selections are saved as a ProjectCategory.

Are there any good libraries that will perform something like this?

Has anyone had a similar situation and can recommend a better layout to perform this?

I have looked into ancestry, awesome_nested_set and other nested set gems, none if which seems to have any views helpers to accomplish this.

Also rails grouped_collection_select does not seem to be able to handle this.