I have had quite a few calls about flooring.  There's not much that I have looked into yet, but here's an article that i found this evening:  http://www.doubledtrailers.com/trailer_flooring.html

Things I am considering in my analysis of products are:

A 1000 pound horse is held up by two 500# footprints.  You don't want to use wood that has any knots in those areas.

Urine is really caustic.  Pressure treated would be a decent choice, and it tends to be cut from logs with few knots.

The rubber mat provides the footing, so the surface of the floor isn't terribly significant.  I would really liek to replace the mats with a flooring product with holes in it for better drying and ventilation.  I have such a mat that I kneel on when working on the truck, but I don't even know where it came from.

Lowes and Home Depot sell a decking product that is all recycled plastic.  It's not cheap and it's heavy, but it's really a good candidate for this application.

Send your suggestions and photos of your trailer to Jeff@KurtzInPA.com

Happy Trails.

Jeff