Having mixed concrete for a few projects, I think it only makes sense for smaller project where the readimix concrete company charges a "short load" and delivery charge. I have done about 1.5 yards with a small mixer, and it *****. Wear's a guy out scooping and filling the mixer. And after all that labor, you still have to screed it, mag float, bull float and trowel it.
For that amount of concrete, it makes sense to just have the truck(s) come and dump concrete, finish it and be done with it. You would potentially save money if you prep all the slab base and forms over a concrete guy coming and prep'ing. (altho it may benefit you greatly to just pay the guy and have it done.....)
While I get the idea of the tent and all that, once the lift is in and usable, you can worry about that. Once a truck is on the lift, you essentially have a "roof" over your head .....
I know you're not in a hurry about getting the lift installed, but it would save some hassle if you didn't have to move it six times before you finally install it. Let alone it is a capital investment that is giving you no return (i.e. use) while it is sitting in the yard rusting.
Regardless, we'll keep the popcorn going.... LOL
I say all this as I would like to see you actually getting to your truck projects instead of the endless circle of shuffling stuff around..........