bisquits

I'm planning on installing panels on my roof soon. I installed panels on a metal shed last year with no problems, but the house roof has recently been slated and looks like this. When I've researched what to install the brackets to that hold the rails that the panels will clamp onto (e.g., these guys), people seem to attach such brackets to the vertical purlins of the roof, which are visible/accessible (like in this video). But my roof has felt over purlins and batten then over the felt, which the slates are attached to. Would the battens be strong enough to attach the brackets for the rails? Or do I need to hunt for the purlins and drill through the felt and risk water ingress??