have swapped ordinary pop up vent over bed for mini heki,straight forward.You would have to know where any structural bits were in foof and also line the hole with timber frame which would be sandwiched in when you screw the two bits of rooflight together loads of good sealant and pull it down well when its warm as the sealant is quite firm when cold.
If it is a straight swap all the strengthening should already be there,roof thickness varies so you may have to cut down the bottom piece's stand-offs to fit,use plenty of sealant as already said and make sure the surfaces are clean.
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