We've had to contend with this for a while now. With our last motorhome, we hauled a 7'x16', V-nosed, enclosed trailer and that, by far, is the nicest, cleanest, most secure, least hassle, way of hauling a Wing, that there is. But, if you're fair weather riders like us, you loose the option of mobility during ugly weather. But, the bike remained spotless and secure at any time we were not using it. OUTSTANDING!
But, because we liked to have options when we're out and about, viewing this fine country of ours, we had to change our game plan. So, we changed motor homes and went with the Hydralift for the back of it. Now, we CARRY the Wing on the back of the coach and, tow our Honda CRV. That way, we got the best of both worlds. But, as you are expecting, your Wing WILL get seriously dirty. Now, doing it as you plan, in the back of a truck, is not quite as bad as doing it our way. That huge, large fan on that CAT C-7 330 HP, kicks up a serious amount of road dust and debris.
So, after some searching around and asking here and there, we found a cover that fits like a glove. It's thick, doesn't flap AT ALL, and, well, it does a fair job of keeping things clean. Now, it's designed to be like a sleeping bag for the bike. It's got cinch straps all over it, about a dozen of them. It would be even better if, we didn't have SIX tie downs holding the bike onto the lift. So, the cover, is somewhat " open ended" at the very bottom, leaving avenues for dust and dirt to travel up and around the bikes un-protected parts.
The cover is called: The Transporter, by UltraGard. It's sold by Wingstuff. AS for cost, it's at Wingstuff for right at $160.00. If one was to alter that cover just a bit, you could cinch the bottom side around all the tie downs and I'm positive it would seal the bike. Now, we traveled with that cover on our bike for a 3000 mile trip and, not one place was "etched" in the paint etc. from this cover. It fits that good. It takes about, 2-3 minutes for install and or, removal. Just an idea.
If I have a choice in the future, I will get a bit larger enclosed trailer and carry a "Smart Car and the Wing". That way, EVERYTHING STAYS CLEAN AND SECURE.