40 gal is a little large for a baby... if it was an older BP it would be fine but for a baby it doesnt make sense. Its also very challenging to get temps/humidity in the right area in glass so a tub is your best bet. A66qt snap top tub at lowes or home depot is about the same size as glass 20L and only costs like 10$... I use these for my babies until they are about 500g then I move them to larger tubs.