Working at Wallops they had several vacuum chambers ranging in sizes from a couple cubic feet to huge chambers an enterer payload would fit in, also had the ability to heat and cool the inside to simulate space conditions.

AMSAT had a lab there for a while, and I worked there where we had a couple thick glass cake covers that would sit on top of a Lexan plate with a sheet of neoprene to seal where you were able to pull out a decent vacuum for outgassing micro-sats.

I was always fearful of them when they were pumped down, but all the engineers and other smart people insisted they were safe.