<VirtualHost  *:80>
ServerName mainweb.example.com
ServerAlias www.mainweb.example.com

RewriteEngine on
ProxyRequests Off

<Proxy *>
Order deny,allow
Allow from all
</Proxy>

 Options +FollowSymLinks

 ProxyPreserveHost on
 ProxyPass /mainweb  http://192.168.1.10/mainweb
 ProxyPassReverse /mainweb  http://192.168.1.10/mainweb

RewriteRule ^/(.*)$ /mainweb/$1 [L,PT]
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule ^(.*)$ /mainweb/?$1 [L]

</virtualhost>