Also - I've been lurking a while and this is my first post :). Great forum you got here!

This is a situation where I would loosen my vent screw.

I have a Thule that fits all my wavesailing rig kit on long trips. Sub 30 it's all good if the box can breathe which mine does. Temps topped 43 on last year's NW run, was concerned and kept an eye it all and everything appeared to survive. Not sure I'd want to do it with boards or regularly cook sails though.

Fact your asking probably says enough but yeah heat and moist is problematic for any long term storage facility, wether in a car/van, rooftop box or even a poorly ventilated storage facility.

Even if it's 30 degrees outside, it'll probably get considerably warmer inside the box.

If you don't have much of a choice and you're willing to accept that your gear doesn't last as long then could be an option and would at least take it out to dry it when back home from a session.

I have a rooftop box that fits up to 7.0 sails. Sails will stay wet in the winter time. The only problem I had was rusty hardware holding the box on staining my white harness lines and white sail.

Grantmac said..
I do this pretty frequently. My roof box isn't super well sealed and I only sail in salt water so I haven't experienced any rot.
Biggest challenge is finding a box big enough. In my experience the only mass produced one is the Thule Combi 600 from the 80s.

In Europe we have a few jumbo sized roof top boxes you can buy that are 140cm wide and up to 290long. I can't post links but if you search for Flensboxx or Surflinebox you'll find them (although I don't expect that's too helpful in Oz.)

darthcitrus said..

Grantmac said..
I do this pretty frequently. My roof box isn't super well sealed and I only sail in salt water so I haven't experienced any rot.
Biggest challenge is finding a box big enough. In my experience the only mass produced one is the Thule Combi 600 from the 80s.

In Europe we have a few jumbo sized roof top boxes you can buy that are 140cm wide and up to 290long. I can't post links but if you search for Flensboxx or Surflinebox you'll find them (although I don't expect that's too helpful in Oz.)

I'm actually in Canada, but still unlikely to find one of those boxes. Fortunately here we have a lot of vehicles which can take a board inside.

One thing to watch for is rusting on the roof of your vehicle. My last one wasn't a very expensive car so I was not as diligent with washing as I should have been, started to rust pretty bad around the rack towers.
Something to watch out for.

Currently, like many North American people, I'm driving a pick-up truck (ute?) and the 6' box is just long enough for wing gear but not windsurfing gear. I had a canopy but mounting a box above that wasn't really possible. So I'm looking at a retractable cover for the box then some racks above it in order to mount my Thule 600. Should let me keep a windsurf quiver and wind quiver on the vehicle without putting anything inside the cab.