I would caution against mounting bike racks on top of a trailer. A friend did this years ago on a tent trailer and found the vibration shook the hardware loose and the whole contraption parted company onto the freeway. The result was very non-reversible! I suspect the vibration on a glider trailer might be similarly problematic.

I would look at solutions on the front of the trailer or around the hitch, as others have suggested. In the USA, double hitches enable using both a hitch-mounted bike rack and a trailer hitch.

Mike