Well then an extra filter might be of help. You could get a filter with the right sized plumbing and put it in easily - with or without the valves. I say this because it would only be filtering any 'stuff' that goes in the bottom inlets. At that point, you may not have to clean it any more often than at water change time.
Cal Spa did something like this years ago - and I had plenty of customers who didn't know the second filter even existed. It sometimes took years to plug it up, since the top-load filter caught most of the dirt.
Glued connections at the filter are more trouble-free than threaded, but be sure to leave a few inches of pipe - free of fittings - in case you need to do a repair later.
