Populate checkbox from params

I have page that list the trails and provides a text based search - see current version here http://ift.tt/1uZA194. I'm adding a form to filter the results of the search e.g. by difficulty, activities, length, allows dogs, etc. I have the filter working, but it's not loading the previously used params in the checkbox fields where the user can select multiple items e.g. allows biking, allows hiking etc. after a search. It's currently only loading the param for the greatest value. e.g. if I have params difficulty=0&difficulty=1&difficulty2 it will only load the page with difficulty 2 selected.

Specifically the :travel_type (radio), :difficulty (checkbox), :dogs (checkbox) and :action_types (checkbox) are having the issue.

Here is a sample URL with params http://localhost:3000/trails?utf8=%E2%9C%93&travel_type=on&max_time=168&max_distance=35&difficulty=0&difficulty=1&difficulty=2&dogs=1&dogs=2&action_types=1&action_types=2&action_types=3&commit=Filter

On reload travel_type 2 was selected difficulty 2 was selected dogs 2 was selected action_types 3 was selected

Here is my view code written in slim

.page
  section.search
    .row
      form.form-inputs.columns.large-6.large-offset-1#search-form action=trails_path method='get'
        input type='search' placeholder='Search' name='query_string'
        button.button-search
          i.sprite-icon-search
  section.filter
    .row
      = form_tag nil, method: :get, class: 'form-inputs columns large-11 large-offset-1', id: 'trail-filter-form' do
        .estimate_time 
          strong Estimate time using
          ul
            li
              = radio_button_tag :travel_type, params[:travel_type], 0
              = label_tag 'Hiking'
            li
              = radio_button_tag :travel_type, params[:travel_type], 1
              = label_tag 'Running'
            li
              = radio_button_tag :travel_type, params[:travel_type], 2
              = label_tag 'Biking'
        div.max_time
          strong Max Time
          div.time
            p
              = '30m'
              = range_field_tag :max_time, params[:max_time], in: 30..240
              = '4+ hours'
            p
          strong Max Distance
          div.distance
            p
              = '1mi '
              = range_field_tag :max_distance, params[:max_distance], in: 1..50
              = '50+ mi'
        div.difficulty
          strong Difficulty
          div
          p
            = check_box_tag :difficulty, 0, params[:difficulty] == '0'
            = label_tag 
              i class='sprite-icon-difficulty-0'
            = check_box_tag :difficulty, 1, params[:difficulty] == '1'
            = label_tag 
              i class='sprite-icon-difficulty-1'
            = check_box_tag :difficulty, 2, params[:difficulty] == '2'
            = label_tag 
              i class='sprite-icon-difficulty-2'
          p
          strong Dogs
          div
            = check_box_tag :dogs, 0, params[:dogs] == '0'
            = label_tag 'Off Leash'
            = check_box_tag :dogs, 1, params[:dogs] == '1'
            = label_tag 'w/Leash'
            = check_box_tag :dogs, 2, params[:dogs] == '2'
            = label_tag 'Not Allowed'
        div.views
          strong Views
          div
            = check_box_tag :views, 1, params[:views] == '1'
            = label_tag 'Has Views'
          p
          strong Activities Allowed
          div
            = check_box_tag :action_types, 0, params[:action_types] == '0'
            = label_tag 
              i class='sprite-icon-horseback-med'
            = check_box_tag :action_types, 1, params[:action_types] == '1'
            = label_tag 
              i class='sprite-icon-ski-med'
            = check_box_tag :action_types, 2, params[:action_types] == '2'
            = label_tag 
              i class='sprite-icon-hiking-med'
            = check_box_tag :action_types, 3, params[:action_types] == '3'
            = label_tag 
              i class='sprite-icon-bike-med'
        = submit_tag 'Submit', value: 'Filter', class: 'button small right trail-filter'

  section.content#trails-find
    .row.find-trails-map
      .large-11.large-offset-1.columns
        .map#find-map
    = render 'trails/trail_list', locals: { decorated_trails: decorated_trails,
                                                 title: 'PUBLIC TRAILS' }