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Using a bento bag behind the stem
Yeah, I thought about that but there's none that fit perfectly so I was going to custom fab a fairing err I mean bento box, that sits down into the Fuelselage to hold gels. But then I noticed Spesh do a purpose built box that goes into the frame where the bottle cage is so that would be much easier than me making something.
those upturned base bar ends would annoy me
You mean on the start bars? I never understood why they did that. I thought maybe because it means some of the brake lever is in front of the bar. I have a set of Magura hydraulic brakes to go on this thing and they have cutouts designed for horizontal base bars but unless you know where to get a Specialized base bar with flat grips, I'm unlikely to change it.
You might as well drop the base bar. Using a bento bag behind the stem is a solution some people use to smooth airflow off the stem, dunno if it actually works though.
Those upturned base bar ends would annoy me, dunno how much is in it but they don't look aero.