[compostqueen]

Lettuce mixes, oriental seed mixes will all do well in a seed tray so your box sounds fine.  I water mine from underneath

I grow Misticanza and an oriental leaf mix like this so I've got fresh salad and stir fries for most of the year 

[Mark's Sussex Allotment]

You could probably grow Kohl Rabi, Pak Choi, Herbs, Chanenay Carrots....

Be very careful in the height of summer though, as mentioned above the will become bone dry in no time and could need watering twice daily.....

Good Luck though

[Muls]

These will stay in my garden so watering shouldn't be too much of a problem. I like the idea of taking one apart to make another bigger ! Thank you for that idea RichardA. Would be left with one good sized and one shallow. If it ever gets warm enough to plant any seeds * big sigh*

[Chrysalis]

Keep the faith, Muls.  It WILL warm up eventually

[devonbarmygardener]

I keep old washing up bowls with holes punched in the bottom for salad stuff - that's always handy.
I keep them by the backdoor.