Would this be safe for a 4,000 mile round trip?

Use and follow the manufacturers instructions and capacity limits on the cargo carrier and you should be fine.

I'm not sure the rear hitch mount was designed to hold that much weight; the roof recommendation is only 145 lb. The rear hitch was designed to pull small trailers so the hitch was to draw the trailer, not carry it. I'd check with your dealer and/or the regional rep. re advisability of having that much weight bouncing around on the back of you vehicle; there may be a clearance problem go up dirt roads....getting it caught on a rock or root could rip it off the CrossTrek. Remember they are recommending a limit of 600 lbs., that's the equivalent of a quarter ton pickup. You could even get stopped for driving an unsafe vehicle........I've seen these platforms on passenger cars and wondered about safety.