Bought this to replace a saggy spring mattress in a caravan.  The fixed bed has an angled corner and it was an easy job to lay the mattress on it, unzip the cover and cut off the corner with a long knife using the bed as a template.  Then simply fold and tuck the cover underneath.  Can't send it back now, of course but no need too, as it is much more comfortable than the old one.  Very pleased.