I'm fairly new to SilverStripe, so please bear with the n00b :)

I've defined a custom page in a new module, which I can edit and view fine, but when viewing, it falls back to the default "Welcome to SilverStripe" template, and not the theme which is configured.

The page itself is totally vanilla:

<?php

	class PaymentForm extends Page {
	}

	class PaymentForm_Controller extends Controller {
	}

I've tried placing a PaymentForm.ss layout in /themes/themedir/templates/Layout which makes no difference.

I've also added the following function to PaymentForm_Controller which does render the page falling back to the Page.ss layout (which is what I ultimately want), but the page titles and nav are all missing.

public function index() {
    return $this->renderWith(array('PaymentForm', 'Page'));
}

I would expect a custom page from a module to render using the standard Page.ss layout without any modification, so it feels like I'm missing something obvious.

I'm running 3.1.2.

Right, so ignore all that and make sure your controller extends Page_Controller.