Stig,
WRONG HOLE! ...and you can quote me on that!

The tanks go in from the back hatch.....It looks like you have glued the intake duct in so that may be a problem. The instructions show how to make a small plywood piece to screw the ducts in so that they can be removed for servicing. Here are pages 17 and 18 from the manual. Sorry about the poor quality...I did a quick scan and paste..........
Tailwinds,
John