A low poly problem? Using Solids to deform a relaxed (tight) mesh - Kangaroo 2 / WB

I am trying to use kangaroo to create a (relatively) low poly triangulated mesh ceiling which wraps the irregular steel structure of the bridge above.

Essentially this is somewhat like a partial shrinkwrap with fixed anchor points at either side - like pulling a tarp tight over the tray of a truck loaded with different items.

My approach so far (which isn't working is)

1 Create a mesh based on the ceiling perimeter with the desired triangle density.

2 Relax the mesh - and bake it and re-reference it to GH

3. Lower the structure (modelled as a group of polysurfaces) onto the relaxed mesh - pushing it downwards (this last step isn't working)

I have adjusted the balloon squeezing sample definition (kangaroo) sucessfully to deform a high res mesh with two polysurfaces simultaneously but with low res mesh I get a spiky look. Is this a low res mesh issue - I understand that the collision is vertex based only.(http://www.grasshopper3d.com/forum/topics/inflation-with-kangaroo-p...)

In the attached definition the collision appears not to work at all.

Any advice on getting it to work or a different approach would be greatly appreciated. I am not sure whether my two step process is helping or whether it's just causing problems.

Thanks,

John