Two glass-panelled aluminum-frame enclosures joined into one temperature-controlled unit sounds like a tricky build. You’ve challenges in balancing air-tightness, thermal expansion, and serviceability. A compressed silicone or EPDM gasket is best. If you are leaning towards silicone, you choose the right hardness and profile. A foamed silicone or EPDM gasket, 40–50 Shore A, will handle it.

Adhesives can seal initially, but they make maintenance painful and don’t handle thermal movement well. Aluminum and glass expand at different rates, so a rigid bond can crack or delaminate over time. If you are joining two cube frames to make them airtight (gasket for flexibility and RTV as backup) combo keeps things airtight, serviceable, and thermally stable.