I ran without the under tray piece for a couple of years, but seeing as the 300's now road ready I'll be looking to stop the road poo from sneaking up into the bits and bobs. I'll probably just fit the 'cheesy' plastic thing we provide and cable tie it on there. I'm a cable tie and gaffer tape expert!
Seriously though, we've never had any complaints, but if you'd like something a little more substantial then it could be arranged, but we're not into making one off (unless it's for my bike

There is the issue of cost of course

Let's see what the rest of you think.