really. send him a pm asking him for tips. in this months freeskier he has a page where he describes how to do a 270 on 270. he could probably help you a lot.
It's easier on down rails/boxes, think about it, you're going up the feature is going down, more time to spin. Flat features require a jump that has a lot of pop and/or spinning REALLY fast and staying focused on the feature when you come around. Also, approaching urban on is a safe way to bail out if you need to.
i prefer 4 disasters, they just give you that much more time. think of it as a 2 with an extra one, because thats all it is really. make sure your head locks onto the end of the rail once your past the 270 rotation.
learn it on a flat down rail with a nice jump on. It's really easy if you have a lot of air. I learned them by disastering a rainbow rail. Then once you get comfortable you can start doing them onto flat rails. I still suck at 450 onto flatbars.
ive never tried one but seeing as a 270 is like a 180, a 4 should be like a three. and trying a fd disaster could work (if ur struggling gettin it around) if your confident you can stay forward enough. however if you want to try a flat box, work on just like huckin threes off knolls and tiny lips - maybe the lip for the flat box but off to the side