PaPaPeng wrote:
Where I am is too cold
for termites.

then it is cold enough for frost heave heave, which is altogether
another nightmare that *I* am trying to fix on an existing attached
garage

I have some old pallets that have been out in the
backyard for the last 8 years. They look a kind of weathered greyish
but no rot.

out in the backyard is not the same as standing on the ground, the soil
will trap moisture and the pallets will rot.

Idealy, you want to put about 2-4" of styrofoam to avoid frost heave,
then whatever support structure you want for the floor. preferably of
something that will withstand the worst contditions. I'm planning
concrete for mine