Yep I think I got ya covered toga10. My suggest is as follows...
MULTI-PURPOSE BASE RACK SYSTEMS
The Thule 400XT Aero roof rack rystem is engineered to fit your 2004 Nissan Altima cartop perfectly and is very quick to install. No matter what gear carriers you plan to mount on your roof, you will need a multi-purpose roof rack base system. The Thule 400XT Aero system includes four 400XT Aero feet, four FitKit 2101 Clips (these FitKit Clips are specific to your Nissan Altima) and two load bars. The 50" load bars are the recommended length for your rooftop. You then mount the kayak and windsurfer carriers to the base rack load bars.
Another really sweet base rack system for your 2004 Nissan Altima is the
Thule 400XTR Rapid Aero roof rack system. Works exactly the same way as the regular Thule 400XT Aero system (uses the same Thule 2101 Fit Kit clips too) except that it uses the elliptical Thule Rapid Aero load bars (the RB47 Rapid Aero bars are the length necessary for your 2004 Nissan Altima rooftop), which are very sleek and aerodynamic offering a more low-profile and modern appearance. You will attach the kayak and windsurfer carriers to the front and rear load bars.
KAYAK CARRIERS
The
Thule 835PRO Hull-A-Port kayak rack is a great universal attachment that uses a j-cradle design for easy loading/unloading of your kayak and attaches to the Thule 400XT Aero load bars and Thule 400XTR Rapid Aero load bars. Includes all hardware, 2 straps, buckle bumpers and a pair of Thule 855 Quickdraw ratcheting tie down straps for securing boat bow and stern. Because this kayak carrier holds the kayak in a semi-vertical fashion it uses up much less load bar space than other kayak carriers, allowing enough room on the load bars to also attach a windsurfer carrier. The all-new design of this carrier also allows the cradle to fold down when not in use, avoiding any clearance issues such as a garage etc.
The
Thule 835XTR Hull-A-Port kayak rack is exactly the same as the Thule 835PRO except the cradles cannot be folded down.
WINDSURFER CARRIER
Finally, I then highly recommend the
Thule 554XT Hang-Two windsurfer / surfboard rack. This is a great sailboard carrier and mounts directly to the Thule 400XT Aero and Thule 400XTR Rapid Aero base rack load bars.