If you're talking about one of those portable ones, about 3 or 4ft wide, they're not really made for seed starting. I'm in Oklahoma and my biggest issue is they get too hot. It can be below freezing & the inside will get up to 70 on a sunny day, so on our random 50 or 60* days seedlings will fry. They also don't retain heat so they won't keep anything protected overnight.
