[dmforcier]

Even before the germ puts up cotyledons it drills for water. Assuming that your starting dirt has some moisture-retaining power, there is little need to try to retain moisture. There will be plenty below.

When I got my 4xT8 fixture I left the dome on as I'd always done with the old 2xT12 fixture and found that the temps under the dome exceeded 105°! Since then I pretty much don't use the dome at all.