Not exactly certain what your mean "Hot House", but I use egg crates on a heating mat to germinate my seed I collect from my Haworthia crosses. The only caution is one must be careful how much water you use because there is no drainage. I guess I could poke small holes in the bottom of each well... too lazy!

Joe
Are you thinking about rooting cuttings from succs?
I don't think cuttings require so much humidity - but for growing from seeds, yes.

Howard
I would imagine that cover is kept off when plants are that size - am I correct?

Rina

When the seedlings grow to a size that won't permit the cover to close they're large enough to move on to their own pot. So the cover is always closed.

I have made a cheap adaptation using an old wooden seed flat and a sheet of twin wall polycarbonate (using fiber filament packing tape to reinforce the joints and a piano hinge for the lid) for growing-on seedlings pricked out from the clump flat (I give the remaining seedlings to other enthusiasts). I pot them singly if they were widely spaced in the seed flat or clump them in individual pots. I tack on an exterior plywood bottom and initially use a heating pad in the early spring until the seedlings are well established. I use this seedling grow-on box outside or in my sun room.

I also use this box to germinate seeds using fiber filament packing tape to seal the joints, again using a heating pad for optimum germination.

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Box with well established seedlings (some grafted)

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Box with well established seedlings - another view]

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Seedlings at various stages of developmen

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Flat with widely spaced seedlings

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Flat with closely spaced seedlings

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Flat with closely spaced seedlings

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Flat with closely spaced seedlings

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Seedlings germinated in pot

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Seedlings separated into individual pots