Okay, I saw a flaw in my plan - a management VLAN. The following configuration should do the trick:
/interface bridge port
add bridge=bridge interface=sfp-WAN frame-types=admit-only-vlan-tagged
set [find interface=ether1-LAN1] pvid=30,99 frame-types=admit-only-untagged-and-priority-tagged
set [find interface=ether2-LAN2] pvid=30,99 frame-types=admit-only-untagged-and-priority-tagged
set [find interface=ether3-LAN3] pvid=30,99 frame-types=admit-only-untagged-and-priority-tagged
set [find interface=ether4-LAN4] pvid=30,99 frame-types=admit-only-untagged-and-priority-tagged
set [find interface=ether5-LAN5] pvid=30,99 frame-types=admit-only-untagged-and-priority-tagged
set [find interface=ether6-LAN6] pvid=30,99 frame-types=admit-only-untagged-and-priority-tagged
set [find interface=ether7-LAN7] pvid=30,99 frame-types=admit-only-untagged-and-priority-tagged
set [find interface=ether8-LAN8] pvid=30,99 frame-types=admit-only-untagged-and-priority-tagged
/interface bridge vlan
add bridge=bridge tagged=sfp-WAN vlan-ids=30
add bridge=bridge tagged=bridge untagged=ether1-LAN1,ether2-LAN2,ether3-LAN3,ether4-LAN4,ether5-LAN5,ether6-LAN6,ether7-LAN7,ether8-LAN8 vlan-ids=99
/interface vlan
add interface=bridge name=MGMT vlan-id=99
/ip address
set [find interface=bridge] interface=MGMT
/interface bridge set bridge vlan-filtering=yes
Hopefully this time it'll work, if not, I will suggest VLAN from another menu - the Switch menu, and will help you with configuring it