Depending on the price, Coroplast can be an excellent skirting material. There's little movement once a trailer is parked and skirted, so any "weatherproof, rigid" material will work to block wind from blowing under the trailer and help retain what little heat is in that area. 1/2" rigid foam sheeting, 1/4" OSB/plywood, vinyl "mobile home skirting" all are good choices.
It really depends on what is available in your area and what pricing each choice has. Coroplast is probably the most durable of the choices, but remember, unless the trailer is parked in the exact same spot, chances are the "cut to fit" skirting won't fit as well if the trailer is moved and leveled in another location for next year. So, if you're moving spaces between use, rigid, expensive skirting may not be the best choice.
2015 F250 6.7l 4x4
2014 Cougar X Lite 27RKS