Moisture problems

[shelbyriffe]

Hello,
I built a tiny home (16'x12') on pier blocks, raising it about 12 inches off the ground. It's framed with studs, joists, pressure-treated cross boards, and plywood. I painted and caulked the exterior, and it has a window AC unit and two windows, but no plumbing inside. While it's been a good house, I face a problem with condensation on the walls and floor during winter. We use an electric oil heater, and I suspect it's a ventilation issue. The floor consists of two sheets of OSB (3/4"), a vapor barrier, and snap flooring. I've confirmed there are no leaks from the roof or walls.

I'm looking for solutions beyond a dehumidifier for winter. I'm considering capping the exterior gap since it's on pier blocks, which might help retain heat, but I worry about air stagnation underneath. I can't keep anything on the floor without it developing moisture. Any suggestions?

[MountainDon]

We use an electric oil heater

....something like one of these? 

Is the floor insulated underneath? The walls? The ceiling or roof?

What are the sources of air borne moisture? Showers? Cooking? and so on.

[MontufarServidone]

If I were your friend and had to give you just one solid piece of advice - insulate the underside of your floor.