Have problem to config both PCC load balance and IP tunnel

I have both RouterOS router at two places:

  • 1st have 2 WAN connections to ISP, I had setup PCC load balance and worked correctly, copied from the example in Mikrotik wiki.
  • 2nd have 1 WAN connection to ISP, and 1 VPN connection to a school intranet, both connections worked correctly

My aim is let computers under 1st router can visit the school intranet through 2nd router, by setup 2 IP tunnels between the two routers (because 1st routers WAN connections are in low bandwidth (ADSL), so I want to setup 2 IP tunnels from each WAN IP address to 2st router (FTTH) for load balance).

I have no idea how to implement it, I tried to setup PCC mangle rules for IP tunnel routing like how I did in 2 WAN load balance, but failed, ping timeout.

I can make it work when 1st router have only 1 WAN connection, I think I must missed something about routing.
Anybody help me?
Thanks.