Solar Bellows Engine, Will this work?

I'm having trouble communicating a potentially unique and simple, stirling engine concept. I might also be missing something, but here it is...
My goal is to make a low energy dense, stirling engine (passive solar) that is also low cost on a kwhr basis. 
To do that I need a very high volume, low speed engine (reduce drag losses).  It would be expensive to build a typical metal engine with say 10" cylinders for 500watt.  However an insulated rubber expanding bellows in place of a displacer and power piston might be an answer.  Here are some sketches to the concept.

This configuration is really simple as the expansion piston and compression piston work against each other.  This is also bad as it fixes the phase angle.  There are fixes to that, the main point is to ask the question of whether or not a bellows engine could be made to work for low temp solar applications?  Without pressurizing the system the cylinders will not see more than 10psi.  Any old inner tube can hold that.  Temperature is an issue 200 deg F will be common.  I think though there is rubber that can withstand those temps.  It may also be possible to insulate the rubber on the inner sleeve to protect it. 
Feedback or criticism would be most appreciated at this point.  Want to get glaring problems out of the way before researching more or prototyping.  Thanks