We have the leftovers from raising tobacco that have been adapted to veggies. Basic set-up is a 2x8 frame, lined with 8 mil black plastic, set on top of 1/2 inch styrofoam insulation with a waterbed heater on top. For the covering, we attached 1/2 inch PVC pipes to form hoops and then cover with a spun polyester cover (some people may know it as Remay canvas). The seeds are sown in styrofoam trays that have 200 "cells" in them that you fill with a soil mixture (think potting soil). Fill the frame with water, float the trays, turn the waterbed heater to high and watch your plants grow. Add liquid fertilizer as necessary/desired. The seeds are sown the first or second week of April and are big enough to plant around Mothers day or Memorial day at the latest. All weather dependant. A week or two before planting, we pull the canvas off to harden the plants. We start tomatos and marigolds this way with good success. Peppers and cabbage don't do quite as well, but we always end up with what we want. Extra bonus, no hole digging or carrying buckets of water either. Dad kept the tobacco setter when he stopped growing tobacco. Dad drives the MF 35 and I ride the setter. We've put out the whole garden before in under an hour (120 marigolds, 100 tomatos, 10 cabbage, 10 or so pepper).
I'm in Southeast Indiana close to Cincinnati Ohio so this may not work for colder climates. It's gotten into the 20's at night before and the plants don't appear to have suffered any damage.