I also saved an old vacuum cleaner with the idea of doing something like that. There are a couple of upsides to using this instead, its light and portable, its much quieter than a vacuum cleaner, where the desoldering heater used to be connected up the temperature (actually power as it didn't have a temperature sensor in the desoldering tool) controller to provide variable power levels to something, like a heater, and this case it was free, someone found it at the dump and brought it back for me.
So that's what they were called, a vacuum easel. I don't have a darkroom set up yet, it would be nice to do that over winter.
Thanks, Ron