The wind passing over the front of the camper and under the box and lifting the box may be large. The sloped shape of the box only helps if the bottom of the box is level to the ground or pointing slightly down in the front. Once the box starts pitching up less air is going over the tapered front and more air is getting under the box (even if it is parallel to the camper roof - the whole roof is pitched up).
My guess is this was barely noticeable early on then got progressively got worse with faster change as time went on because more and more air got under the box and the forces pushing up on it kept increasing as the bend angle increased.
With the racks attached directly to the sides of the top without the use of rails there is nothing to prevent the box from pivoting on one of the crossbars and lifting up on the the other (which appears to me to be what is happening - it appears to be pivoting on the back crossbar).
If the rails were in place that load would be distributed along the length of the rails making this less likely.
If it were my camper I would remove the racks and install rails and make sure they are securely fastened to the roof framing and then make sure that the roof is flat when you are done. Once that is done you can put the towers on the racks and put the crossbars back on.
I would also try to put long rails on and try to put the crossbars and the box as far back from the front of the camper as possible.
Hopefully the bend is not permanent but my guess is that it may be which will make getting the roof flat again a bit of a trick. Long rails will help with that.
Regards,
Craig
Edited by ckent323, 05 March 2015 - 05:01 AM.