There's no "decision" to be made.

Whatever God provides we will use. There's a lot of wisdom in what everyone has said about a trailer. I priced a new one just to have a frame of reference, and found a Wells Cargo: CW 1411, 7’ x 14’ – Extra 6” height, White. $6,500 + shipping from Kealakekua. Out of my price range unless God just drops 7 grand on us for this... and He could.
Got a call today from somebody offering a large panel van, no windows, for $1,500 but I don't think it is big enough, and not able to handle the weight, I fear.
My ideal solution would be a steel shipping container parked on site, but (so far) the school is less than enthusiastic about allowing that.
"God is excited to show you mercy. He rises to give you His compassion." (Isaiah 30:18)
"For surely, O LORD, you bless the righteous;
you surround them with your favor as with a shield." (Psalm 5:12)