Are there any pro's/cons to a RTT on a Cap?

I'm planning a cross-country trip, coming up this spring. I always been loosely planning on buying a cap/rack combo and mounting our roof top tent to the cap. That way everything in the bed stays nice & dry and I have the tent right there, ready to go.

It struck me that I don't often, if ever, see this setup in pictures or threads and I've started to wonder if that is for a good reason. I almost exclusively notice people using RTT's with bed racks vs caps. Like these ones.

I assume the fuel efficiency will be worse with a RTT on the cap, but does anyone have any first hand experience on exactly how much worse? Are there any other pro's or con's anyone can share?

P.S For reference, I have a DCLB Quicksand + Smittybilt overlander tent. I am clearly in the market for a cap, too, just sayin, if anyone has advice in that regard or is looking to sell!

 

i can't speak to any reasons not to put the tent on a cap other than possibly the weight of it being too much for a cap, but can't say that definitively. I know some caps offer a reinforced version.

As far as MPG, expect to lose 1-2MPG depending how you drive and the conditions.