Mike,
I build my molds in a similar fashion to keep the weight and material cost down only I use just the upper and lower. As stated before, you should not have a problem as long as your inside caul does it's job distributing the pressure.
The bending pipe: I made and electric one using an old mobile home water heater element and two timers...just off/on/off repeat cycles to regulate temps, The torch works ok but hard to regulate temp. Some builders are using an electric
Bar-B-Q charcoal starter and bending it to fit in the pipe.
And order some supersoft to help keep the wrinkle out of your sides. I spray the wood the night before bending and it helps! Even some more flatsawn woods bend with a lot less cupping.