Car topping vs Trailering Kayak Fuel Mileage

What would likely result in the better fuel mileage over a 100 miles driving with 85% at 60 mph highway driving; car topping a kayak or trailering it on a small trailer behind a MK4 golf.

I would imagine trailing would net better mileage but really over 100 miles the difference wouldn't be worth any thought as far as I'm concerned. I would go with whatever is more convenient unless it will be a very regular occurrence.

Based on my experience I think it depends on how the kayak is mounted on the roof. With my Mk IV, BEW Kerma tune:

Good general highway with clean roof. 47 or better mpg US
Same with small aerodynamic rocket box. 45 mpg US
Canoe on roof. 42 mpg US
Utility trailer about 800 lb total. 45 mpg US

Now if it was my Mk VI Wagon before fix

Nothing on roof, no trailer 46 mpg US
Rocket box on roof 43 mpg US
Canoe on roof: 37 mpg US
Canoe on trailer: 37 mpg US
Kayak on roof in kayak rack and bicycle on rear rack: 35 mpg US
Kayak attempting to be aerodynamic: 42 mpg US

Except the clean roof mpg the above is measured based on single tank fill ups running at 60-65 mph on two lane roads

You are going to be splitting hairs, really. The trailer will go through the air easier, but will add some drag due to frictional losses from the trailer's tires and axles, not to mention whatever the trailer weighs.

I would just go for what is easier/more convenient based on how often you are going to be using it.

I have had roof racks on my cars in the past, and found them a pain to take on and off... much easier to just lash a trailer to the car in my opinion. But, if where you are going makes dealing with a trailer a different kind of pain...

Just know that no matter what, your car will still net some pretty good fuel economy. My WORST tank ever in my 2000 Golf was 39 MPG.... and that was with a 1991 Jetta on a tow dolly behind me crossing the Appalachians.

Idunno about there but in Kalifornia the speed limit with a trailer is 55.

Parking can be an issue at some lakes. Trailer won't make that any easier.

pull out the passenger seat with two 13mm nuts and bring it with, inside the car

If its 50 mpg vs 45 mpg, it will cost you an extra $.66 for every 100 miles with diesel at $3.00 a gallon.

Thanks for all the replies and thoughts. It's a 14' kayak, so it can't go inside with the driver seat pulled. I'd never do that even if it would fit inside.
The trip is 100 miles one-way. I just used that distance in my scenario so y'all would have something to work with and so I didn't get replies stating it depends on the distance. I hope to be doing this trip a lot.
The trailer is more convenient and I hate the noise from the kayak roof rack. I'm going with a trailer even though it will cost more to cross the bay bridge tunnel.

In California I would go without a trailer personally. I road tripped out there last year and the hassle was much greater especially with the bridges all costing more and the speed limit of 55 which they do choose to enforce randomly. If it's regular enough consider a box for it up there in a convenient location. I know they have a few to choose from around there.
The one benefit toa trailer is that you can add a few hundred pounds and the weight isn't on the car, so you can take the campsite equipment and drop it, which is just my style, so I understand your desires.