I have only just finished sowing my runner beans in pots in the tunnel today(Lady Di and Enorma - 600 of each) and when I plant them out at the start of June, I will sow another bean alongside the young plant. This should give me 8 plants to each 4 cane wigwam and extend the season without taking up more space.
As regards hardening off, I just throw fleece over my toms, cukes and pepper plants, then open the doors at both end of the tunnel and let the wind at them - would take me all day to empty the tunnel and bring them all back in again.
However, in the garden at home, I do harden off my plants from the greenhouse before planting out. They go into a cold frame for about a week - lid up during the day and closed at night.