Im currently living full time in a 30 foot travel trailer. I bought one with the " polar" option. That means the underbelly is insulated and covered, and the holding tanks are heated as well. I'm looking for ideas to keep the wind from blowing under my trailer. Needs to look good, and be removable.

Square hay bales.  By them cheap and stack them deep .  Really, jst around the perimeter should be good.

I have a similar camper with slide-outs.  Lots of gaps and lost heat in those cracks.  Caulk them sfrom the outside and peel them ff in the spring.

Anything that will block the wind will help a great deal.

For something that is quick and easy to use and easy to take down and transport try some courregated galvanized sheets of "tin".

I knew a family of three that spent a winter in such a unit.  They used plywood.

Yup. Skirt it

Look to the "mobile home" industry.  They have a "top channel" that can be attached permanently that you probably wouldn't even see from a distance.  Then you can use cheap interlocking vinyl soffit cut to size.  It locks together for the run, then disassembles into small(20-24 inch?) sections for storage.  Very lightweight.  The bottom channel could be cut to workable lengths and attached to the ground with gutter spikes(reusable) if on the ground or maybe a bead here and there of some caulking if on pavement.  It wouldn't hurt to incorporate a vented panel on at least each end to cut down on moisture and condensation underneath...

I can give you more info if you want to message me....
(NOT a salesman- worked in or around the mobile home industry for the last 30 years...)

2" XPS - paint as needed.

Hay bales.

you could use lexan/plastic/1/4 plywood, mount it onto the frame with a hinge so then you can fold it up under the trailer for transport crawl under and unhook and let it swing down and make a skirt

Not sure if Coroplast would be rigid enough, but it comes in 4'x8' sheets and is thin and light and relatively cheap.

Snap-on vinyl skirts are commonly used.  However, they are generally custom made.  Most RV dealers can give a contact recommendation.  Otherwise, go with straw bales.

Come to find out they do not allow any type of skirting at the rv park. I like full timing  but I'm worried about the winter in Mo. I have been looking into getting a true RV. Something that a built in underbelly with insulation and more storage.