Can I extend my Visa on Arrival in Thailand for 30 days at Chaengwattana, and do I need to show an onward air ticket?

The user, currently on a Visa on Arrival from the Netherlands, is seeking guidance on whether they can extend their stay by 30 days at the Chaengwattana immigration office. They are also inquiring about the necessity of showing an onward air ticket for the extension, and whether their prior residence in Thailand on a work permit might affect their chances of receiving this extension.