Canopy for camping on top of

Hi, I have a dual-cab Hilux with genuine alloy HD tray that I will get a rear bar & plate roof-rack (Maxi-Rack style) added, to form a base to build on security screen doors & canvas covering. The idea is to use the top for a 8' long mozzie/dome tent with mattress inside; length of the ute tray is 6'. Is 2' of cab overhang OK for the rack, or is there going to be more wind resistance/noise, & is it better to go with a 6' rack & concertina the done tent to fit? The rack may get used for camping for a weekend every 2 months, so a bit of a squeeze for camping then may be bearable compared to to an increased fuel bill. Cheers.