I have been contemplating skirting for a month now. probably a month too long being it is november now!! but anyhow I have seen a couple methods.
1 - Vinyl skirting. easy to work with, turnbuckles and snaps to attach, nail to the ground, matches trailer, can move the trailer and keep the skirting.
2 - Plywood. not the greatest looking but sturdy, kinda redneck looking
3 - Insulation board. kinda flimsy, reflective, temporary. might be cheapest.