Man, you dodged the bullet on losing birds for sure. Good thing they were turkeys and not bantam chickens trying to hold that tractor down.
After we made our first one that was so big and heavy, we wanted to go lighter, but so many people in our area had lost birds and houses because of normal winds that we have all the time or with our usual thunderstorms, that safety was a huge concern for us if we tried to build lighter housing. In the end, we decided that we'd rather have heavier housing than lose birds. The a frames we build now are lighter than our other designs, but they are still made with 2x4 lumber and pretty heavy, while the wide base makes it easier for even the small pens to stay put in the wind. Around here, it we don't even need a storm to send things flying across the pasture. A normal windy day with 30-40 mph winds when a cold front is moving in or a warm front coming up from the Gulf is enough to do plenty of damage if we let it.