I gave up using waterproof trousers (too much messing about and hot where I dont want to be hot) and moved onto a rain skirt and gaiters. Much prefered, comfortable and cool, on and off in 5 seconds. I've now moved on to a long waterproof coat, again using gaiters. Easy to put on and off as well.
I can understand your problem, my legs are not long and they never fitted well, the trousers I used also had long zips so I couldnt shorten them.