Hi

We have the 2830 router installed on a very slow ADSL2 line. We've got a 4G dongle with plenty of data use as a 2nd WAN and help to load balance. What is the best way of setting up to use both of these WANs together.

here some links if helps you
http://www.draytek.com/index.php?option=com_k2&view=itemlist&task=category&id=383:route-policy&Itemid=293&lang=en
http://www.draytek.com/index.php?option=com_k2&view=item&id=5181:policy-route&Itemid=293&lang=en
https://www.draytek.co.uk/archive/kb/kb_load_balancing.html

Another way which worked for me in past ... at load balance / route policy, can tik only the wan you want (1,2 or 3) and then move it on top at the right side of the page
That should divert all traffic to this specific wan (work 24/7) and the other wan (adsl) can be use if the 4G fails or vice versa (the other way around)