truma

Hi guys, I wonder if anyone can help, my T6 is fitted with a gas Truma heater installed under passenger seat, not used it yet but may need it soon due to cooler season coming. I have a brochure which mentions removing/opening a "cowl" before starting it up. I don't know what/where to find this...

I'm looking at fitting a ebrspacher or webasto night heater and wondered if anyone has fitted either and can recommend location to fit and which one is best to go for, I currently have rib bed and insulated but no kitchen unit fitted as yet