I pored 2 cement pads and park mine on them from Nov - April outdoors. Flat spots do not happen on radial tires this is folklore from bias ply tires.
it snows here and the sun doesn't have the ability to reflect it is just passing over us ROFL..
In reality you only keep them for 4 years and get new ones.. so storing them in any particular fashion is what we call MCOCD from another forum... I store my boat trailer the same way and never have issues in 4 years.
as always whatever let's you sleep at night
) make sure you have a good tire that is rated for your trailer. Don't go cheap as it won't matter in the summer at 100 degrees flying down the freeway at 70mph...