Exactly!
If your bed is painted to match the truck, pull the fenders off, trim the hole, add reinforcement as needed, if you have fabrication skills this will be easier than bed replacement, cheaper than repaint to match truck, and you wont need to find a good dually bed within driving distance!
If you haul those trailers frequently your money would be much better spent on a set of air bag helper springs, not only will they keep your tires from rubbing, they will also give you more stability and keep you from "draging your ass"
Then again...my SRW trucks tend to squat under load, even my factory dually never squatted the way a 250 or 350 srw would, but still, assist springs are nice to have.
Then saw the wheel opening bigger until you find the right bed...if it's already junk you can't make it much worse.
Nick