Were I to wish to trailer my boat for a very long distance, and do so at highway speed, I would first put on the playpen cover, then cover the entire boat with a heavy canvas tarp, making sure to tuck under at the front. You can get the tarps at one of the big box hardware stores.
As an alternative, I could have my local marina "blue-top" it for me. That's the shrink wrap plastic they use for storage. Tough stuff.
That's just me. I know that lost of folks trailer with their factory playpen covers.
Be advised though...
If you have the kind of playpen cover that attaches to the front of the DECK, it's going to be pretty good at keeping wind out of the interior of the boat.
If you have the kind that attached to the fencing, even at the front... Well I just don't know. Maybe it works, maybe it doesn't. I honestly couldn't tell you.
THAT'S why I like a supplemental cover, to absorb the abuse.