I have this working with several Fortigate models and Meraki MX.
Fortigate setup on 5.2. It also worked on 4.0 but the screens are different.
Ipsec Tunnels
Create New
Custom VPN Tunnel
Name xxx
IP Address from Meraki dashboard
select Interface
Uncheck Nat Traveral and Dead Peer
Enter Pre-Shared key
Remove all Phase 1 Proposals except "3DES SHA1"
Check only DH group 2
Change key life to 28800
Enter name for Phase 2
Enter local and remote subnets for Phase 2
Click Advanced
Remove all Phase 2 proposals except "3DES SHA1"
Uncheck PFS
Add static route for remote subnet
Add two firewall policies two allow traffic to and from tunnel.
The Meraki side is simple.
Site-to-site VPN.
Add non-peer.
Cable modem setup
(This was required on one Meraki unit but I have several working with no change to the cable modem.)
Forward ports 500 and 4500 to Meraki.
Update: VPN setup between Fortinet and Meraki - Part 2
