Is it possible to convert to thermo cool?

That might be it.

BUT

A local shop around here has a huge display outside the walk-in they keep the really expensive stuff in and they modified it with a thermo unit, it always reads 68-70 in the summer even when its frigging hot out. Its all glass, 3 sides, 6 feet high, 6-8 feet wide a foot to two deep. The glass doors are no way 1/4 inch, probably double strength at best.

So its possible.

Chas