RbOH and CsOH are INCREDIBLY strong bases. Both of them will attack glass, CsOH moreso than the rubidium version. I will also warn that they are very expensive and you will not be able to isolate the metals from their salts. Both of them will react violently with the slightest hint of moisture in the air, and Cs will catch fire immediately if exposed to the atmosphere. Unless you have a high quality chemistry lab at your disposal, you have almost no shot at isolating the metals. (Now if you just want the metals, check out my link to Juergen Bauer's website in the links section. He sells rubidium and cesium metal).