The idea of a tranny blanket is good, but think that a heavy carpet remnant would be suitable too. Depending how you build the cradle for it perhaps some SS mesh as a liner? My only concern was for the integrity of your used, massive bell jar. Another thing I thought of was a diffusion pump for the volume you are dealing with. You can find old Veeco Helium leak detectors at auctions, even ebay that have diffusion pumps in them and seen them for a few hundred duckets although Diffusion pump oil is pricey. A source for compressors might be a restaurant refer? The thing is I don't think you need to to achieve the vacuum between galaxies to do what you want depending on your fluid for impregnation.

Be Warm and holler if I can help bounce some ideas around.

PJ