Creating a RSS feed for several selected categories

If I do this http://www.website.com/index.php?page=search&sCategory=123&sFeed=rss

I can create a RSS feed for a particular category. But what if I want to create a RSS feed for several selected categories? is it possible? OSClass version is 3.3.2

I didnt find a short or integrated way to do it, so I coded it.

<?php


define('ABS_PATH', str_replace('\\', '/', dirname($_SERVER['SCRIPT_FILENAME']) . '/'));
if(PHP_SAPI==='cli') {
    define('CLI', true);
}

require_once ABS_PATH . 'oc-load.php';

$mSearch = Search::newInstance();

$array_categorias = array("16","22","23","24","31","33","43","102","119","121","122","123","124");

$aItems  = $mSearch->doCustomSearch($array_categorias);

View::newInstance()->_exportVariableToView('items', $aItems);

 // FEED REQUESTED!
header('Content-type: text/xml; charset=utf-8');

$feed = new RSSFeed;
$feed->setTitle(__('Latest listings added') . ' - ' . osc_page_title());
$feed->setLink(osc_base_url());
$feed->setDescription(__('Latest listings added in') . ' ' . osc_page_title());

$contador_items = osc_count_items();

if(osc_count_items()>0) {
    while(osc_has_items()) {
        if(osc_count_item_resources() > 0){
            osc_has_item_resources();
            $feed->addItem(array(
                'title' => osc_item_title(),
                'link' => htmlentities( osc_item_url(),  ENT_COMPAT, "UTF-8" ),
                'description' => osc_item_description(),
                'dt_pub_date' => osc_item_pub_date(),
                'image'     => array(  'url'    => htmlentities(osc_resource_thumbnail_url(),  ENT_COMPAT, "UTF-8"),
                                       'title'  => osc_item_title(),
                                       'link'   => htmlentities( osc_item_url() ,  ENT_COMPAT, "UTF-8") )
            ));
        } else {
            $feed->addItem(array(
                'title' => osc_item_title(),
                'link' => htmlentities( osc_item_url() , ENT_COMPAT, "UTF-8"),
                'description' => osc_item_description(),
                'dt_pub_date' => osc_item_pub_date()
            ));
        }
    }
}

$feed->dumpXML();
?>

I also had to add a couple of custom methods to the search model

public function _makeSQLCustomCategories($categories)
        {


                $cadena_select = DB_TABLE_PREFIX."t_item.*, ".DB_TABLE_PREFIX."t_item.s_contact_name as s_user_name,";
                $cadena_select = $cadena_select . DB_TABLE_PREFIX. "t_item_description.s_title, ";
                $cadena_select = $cadena_select .  DB_TABLE_PREFIX. "t_item_description.s_description";

                $this->dao->select($cadena_select);

                $this->dao->from( DB_TABLE_PREFIX.'t_item' );                       
                $this->dao->from( DB_TABLE_PREFIX. 't_item_description');

                $this->dao->where(DB_TABLE_PREFIX. 't_item_description.fk_i_item_id = '. DB_TABLE_PREFIX. 't_item.pk_i_id');

                //$this->dao->where(DB_TABLE_PREFIX. 't_item.b_premium = 1');
                $this->dao->where(DB_TABLE_PREFIX. 't_item.b_enabled = 1');
                $this->dao->where(DB_TABLE_PREFIX. 't_item.b_active = 1');
                $this->dao->where(DB_TABLE_PREFIX. 't_item.b_spam = 0');

                $where_categorias = "(";
                $contador_categorias = 0;
                $tamano_categories = sizeof($categories);

                foreach ($categories as $categoria)
                {
                    $contador = $contador + 1;
                    $where_categorias =  $where_categorias.  DB_TABLE_PREFIX. 't_item.fk_i_category_id = ' . $categoria ;
                    if ($contador == $tamano_categories)
                        break;                  
                    $where_categorias = $where_categorias . " OR ";
                }

                $where_categorias = $where_categorias . ")";

                $this->dao->where($where_categorias );

                $this->dao->groupBy(DB_TABLE_PREFIX.'t_item.pk_i_id');

                $this->dao->orderBy(DB_TABLE_PREFIX. 't_item.pk_i_id', 'DESC');


            $sql = $this->dao->_getSelect();
            // reset dao attributes
            $this->dao->_resetSelect();

            return $sql;
        }

        public function doCustomSearch($categories, $extended = true, $count = true)
        {

            $sql = $this->_makeSQLCustomCategories($categories);
            $result = $this->dao->query($sql);

           if($count) {
                $sql = $this->_makeSQLCustomCategories($categories);
                $datatmp  = $this->dao->query( $sql );

                if( $datatmp == false ) {
                    $this->total_results = 0;
                } else {
                    $this->total_results = $datatmp->numRows();
                }
            } else {
                $this->total_results = 0;
            }

            if( $result == false ) {
                return array();
            }

            if($result) {
                $items = $result->result();
            } else {
                $items = array();
            }

            if($extended) {
                return Item::newInstance()->extendData($items);
            } else {
                return $items;
            }
        }