Have just purchased a new D40 STX and fitted a Carryboy canopy. As well as the tailgate area, the tub has large holes in the top corners at the front of the tub that need filling with sikaflex or similar, as well as some other various holes and poorly sealed joints. To seal the tail gate sides we used 6mm x 50mm insertion rubber stuck to the side (similar to what Paul did with the flat aluminum) and a length of 6mm x 15mm affixed across the bottom of the tub. Seems to work ok, but it will get a real test in May/June when we go via the dirt from Broken Hill to Cape York and return in May/June. The pressure vent/open front window works reasonalby well on our caravan but whe surrounded in bull dust or dust from passing vehilces some dust does get sucked/forced inside the van so I'd think it'd be the same with the canopy. When travelling busy dusty roads we leave the vans pressure hatch closed.
cya
Graham