Ok I found another solution that it could help , the first solution I already posted it here before ,
The second one is:
********* First *********
add this code
<div class="mobilemenu visible-phone">
<jdoc:include type="modules" name="<?php $this->_p('slide-menu') ?>" style="raw" />
</div>
inside \templates\t3_blank\tpls\blocks\header.php
--------- like this file --------
...
.......
<div class="nav-collapse collapse <?php echo $this->getParam('navigation_collapse_showsub', 1) ? ' always-show' : '' ?>">
<?php if ($this->getParam('navigation_type') == 'megamenu') : ?>
<?php $this->megamenu($this->getParam('mm_type', 'mainmenu')) ?>
<?php else : ?>
<jdoc:include type="modules" name="<?php $this->_p('mainnav') ?>" style="raw"/>
<?php endif ?>
<div class="mobilemenu visible-phone">
<jdoc:include type="modules" name="<?php $this->_p('slide-menu') ?>" style="raw" />
</div>
</div>
.....
..
as you can see I added another menu with a class called "mobilemenu" for more css and I added the "visible-phone"
********* Second *********
now with the css file you are using add this line :
.t3-megamenu.animate.fading {display: none; visibility: hidden} - to hide the main menu
********* Third *********
now you have to create a PHP block file and call it "slide-menu.php"
and add this code
<?php
defined('_JEXEC') or die;
?>
<!-- Mobile Slide Menu -->
<nav>
<div>
<jdoc:include type="modules" name="<?php $this->_p('slide-menu') ?>" />
</div>
</nav>
<!-- //Mobile Slide Menu -->
********* Forth *********
Add a position inside the templateDetails.xml
<position>slide-menu</position>
Thats it , now you can use html module or any menu module and set the position to slide-menu and you are ready to go , with some css you should be good
Have fun guys