Living Soil and Indoor flower bed?

I agree with others, if its elevated and whatever runoff you do generate is getting collected should be OK. I would not trust my tents drip matt to hold that much moisture without failing over time. try finding house wrap plastic that very thick and that should help if you can find a solid piece of plastic for this. One thing to note is that the plants will be massive will all the extra root space and may grow out of space inside the tent, that container is going to be taking up some top real estate. Some LST and HST will need needed or it will outgrow the space and not work. Autos might be a option as they tent to stay smaller or just flip to flower sooner with photoperiods. Good Luck!