I'd start by going with the solar fan. They work, even when there's no breeze, so that going below can be tolerable on even the hottest days. We've had ours for 12 years, and have had to replace the batteries (drumroll)... once. One of the reasons they come with fans is that their low profiles keep them from moving as much air as standard cowl funnels. A question, however: are you replacing the dorade boxes or just the ventilator funnels? Replacing the boxes will likely leave marks on the deck where they were. The marks will probably not be covered by the new vents, so you will have to repair, paint over, or otherwise hide them If you are just replacing the funnels, or only have funnels (no dorades) and are simply trying to keep things dryer below, the flush ones should be easy to install. I would get the fans, though.