@mandolls -- Geof, about the fall planting, I totally agree with Chelle; the timing is tricky and although I keep trying it hasn't (to date) worked out all that well for me. As Chelle said, though, by continuing to plant throughout the growing season you will have earlier -- and later -- harvests.
As far as the UP never getting really hot in the summer... we sometimes have summers that are very hot and humid (or at least they seem "very hot" to me, maybe not so much to a lot of people), but the last 2 summers were unusually cool (very, very rare to have any nighttime temps over 70) and this summer is looking like more of that same trend. I always put the plastic around the tomato cages when I first put them out, to give them some extra early warmth and protection from the wind, but generally remove it around the beginning of July. Last summer I planted the tomatoes fairly late and June was a pretty warm month, so I never put the plastic up -- which I regretted the entire remainder of the summer because it never really did warm up like it should have and our tomatoes ripened really, really late. So this year, although I again didn't get the plants out of the GH until mid June, I decided to use the plastic even if I have to take it down after just a few weeks. So far it looks like it will be staying up for a while, at least... and actually, even when the weather has been pretty hot the plants have never seemed to have any problems from being in their little "hot houses." The top is fully open, and the ground is mulched, and they tend to grow like crazy with the protection. (I originally started covering my tomatoes this way when I was using round cages made of fencing; at that time I used some big semi-clear plastic bags that I partially cut on the closed end so they would be ventilated on top, then just slipped them down over the cages and used twine to hold them on. Now with the wooden cages it's pretty easy to wrap the plastic around and just staple it on.)
Still waiting to win the lottery so I can get a greenhouse that will cover the entire garden... or maybe the entire garden, yard and house!!
The wooden cages are 2 feet by 2 feet square (approximately), and about 5 feet tall; I've had them in different arrangements over the years, but this year have them in rows of 4 together, with the plastic wrapped around the group. (I use plastic that was used to cover the GH for the winter.)
