Here is something concrete:
| cutomer1 LAN | ipsectun1 VLAN1
|_192.168.1/24_|============| STRONGSWAN |----------|_customer1_hosted_|
| |
| VPN |
| |
| 192.168.1/24 |============|__GATEWAY___|----------|_customer2_hosted_|
|_cutomer2_LAN_| ipsectun2 VLAN2
Should be better... hopefully.