That's a really interesting idea! I've had success with toilet roll tubes, now planted out and growing well, but it is hard to keep our soil damp if I sow them direct. A plank might gdo the trick - but I would think our slugs might find it a useful home as well!
I sowed in April and immediately put a plank of wood over the row, keeping it moist, 2 weeks later I lifted the plank and hey presto a row of Parsnips that are so full I actually need to thin them.
Normally from a row I get maybe 10 germinating, this time there must be 100.