It sounds like the Residence is a boat anchor
I know, we all have our reasons.
Dirt floor? Rototill a few gallons of ox blood into it and then use concrete-finishing tamper/propellor/vibrator to finish it. Not that I've ever done it, that's from antiquity.
How level will the trailer bed be? You lay down swing-door material and shim it to get maybe ±64th or 100th of an inch. It would be good to have a plate more accurate than you want the chassis.