wla wrote

- ports 1-3: vlan 111, 112 and 113

Any port which is a member of more than one VLAN is a trunk port by definition. Note that the 802.1q standard does not use the terms "access port", "trunk port" or "general port". There are only ports which either belong to one VLAN only (that's then called the Primary VLAN) or which belong to more than one VLAN (those ports are then just members of more than only their Primary VLAN).

If not, is it possible to assign multiple 801.1q based vlans to a port?

See above. 802.1q requires that such assignments are possible, else the device is not conforming to 802.1q. So the answer is: yes, TL-SG108PE can assign a port as a member of multiple VLANs and you can do that with any/all ports.

Just make sure you install latest firmware which allows you to remove ports from VLAN 1 (and do so with non-trunk ports), this will save you lot of headaches.