Tengo problemas para almacenar los valores de las casillas de verificación en la base de datos de mysql (solo el último valor se almacena en la base de datos). ¿Cómo puedo arreglar este código para almacenar todos los valores marcados?

<label class="q" for="q1">Which, if any, of these activities did you do on the Internet in the last 30 days? 
</label><br><br>
<input name="q1[]" type="checkbox" value="a1">Used e-mail<br>
<input name="q1[]" type="checkbox" value="a2">Used instant messenger & chat room<br>
<input name="q1[]" type="checkbox" value="a3">Made a purchase for personal use<br>
<input name="q1[]" type="checkbox" value="a4">Downloaded/Played a video game<br>
<input name="q1[]" type="checkbox" value="a5">Obtained news/information/current events<br>
<input name="q1[]" type="checkbox" value="a6">Looked for employment (Used classified listings)<br>
<input name="q1[]" type="checkbox" value="a7">Looked for recipes<br>
<input name="q1[]" type="checkbox" value="a8">Downloaded a movie<br>
<br>



<?php

include('config.php');

$tbl_name="temp_members_db";
$q1=$_POST['q1'];
$sql="INSERT INTO $tbl_name(q1)VALUES('$q1')";
?>