Chromo bends nicely. To do that well you would need a JD squared type bender with a 1.125 die. There are ways of bending other than that, but in this case you have a short tube, a tight linked bend. There are lots of online plans for this kind of bender. There is a lot going on with the seat tube, so you don't want to add to the stress by doing something like a hot bend.
That seems unnecessary to have a double-bend in the seat-tube. It would appear that having a single-bend to tuck the rear-wheel up close is all you need. The angle of the seat-tube at the seatpost may then be aiming back more, but that's find if you want to maintain similar position over the BB anyway.
I have an old custom steel frame, a Clark Kent, that has a bent seat tube, but I don't know how it was done. that was kind of their claim to fame, gets you a steeper seat angle (78 deg.) but it still has sharp road bike geometry in the front, not like a tri bike. I like it.
henry james. they are listed under aero tubing. there are two versions. one is round at the bottom and the other is ovalized. they are a bit tougher to use than a regular tube but it doesn't take too much figuring to get it right. One thing to watch out for is that it stays aero pretty high up, so when building a small frame you usually have to extend the ST so that there is enough room for a seatpost before it gets aero.