The blocking of cooling is over-emphasized. The Westy uses a 2-speed fan that is shrouded so it pulls air through -- not relying on vehicle speed. The capacity, if every thing is working correct & good condition, is sufficient such that the minor flow disturbance (more than actual blocking) should be of little consequence except perhaps in desert trips.
Some headlight difusion might occur, but I would hope you have a good set of fogs down at bumper hieght anyway. Nowdays, you can rarely get to high beams anyway and good fogs will outdo the OE low beams. The blockage on vehicles with headlight guards and front bumper grill guards doesn't seem to be that significant anyway. 3R + 1F with the rack
Chuck (CA) recommends seems reasonable. The site
backcountrymedic recommends (2/25/05) has numerous configurations, including the ability to put 4 on the rear w/o a trailer hitch mount (using his multipurpose rack and 4 bike mounts). You've got a factory roof rack that could hold a couple and can get other acceptible roof racks that don't require drilling/weight on the pop-top; the same site has side ladders to reach them. There is an entire topic devoted to <Aftermarket (only) Roof Racks> in this forum.
Nobody can make this decision for you -- you have sufficient information to pick. The Westy wasn't built to carry bikes outside; anything to adapt will be a compromise. Visit (or arrange returnable orders) with these vendors to examine them in your circumstances.
