Why do you need any tins at all? a black painted box will heat up the air in it sufficiently. If you can find a surplus double glazed unit and insulating the box with polystyrene or even corrugated paper will trap more energy in the collector but the wood thickness is sufficient and on a sunny day single glazing will work well.
The key to dehydrating is large volumes of warm, dry, air, not high temperatures, so the less resistance to air movement the better.