However, I also need to start lots of tomatoes and peppers. I was planing to heat the frame with a heating cable under sand. Would this make water evaporate so fast as to make this watering system impossible?
Shouldn't. Yes, it can evaporate water but it should stay contained with the frame and rain back down, like a terrarium.
"You must be the change you want to see in the world." "First they ignore you, then they laugh at you, then they fight you, then you win." --Mahatma Gandhi
"Preach the Gospel always, and if necessary, use words." --Francis of Assisi.
"Family farms work when the whole family works the farm." -- Adam Klaus
His brain is the size of a cherry pit! About the size of this ad: