500Km = 310 miles, one way...
If you can pick it up that day and save driving 600+ miles, wouldn't you?
If you can make a belly bar work then go for it. I've seen far hinkier ways to temporarily secure a camper in a truck bed.
In fact I've used one: I used some stake pocket tiedowns I found on Craigslist the day before I went to get it, and threw 2" ratchet straps over the top of the camper because I didn't have anything short enough to go from the tiedown points. Drove extra-careful, avoided potholes, and still using the camper almost 7 years later.