Some years ago I used a rear carrier with a bundle buggy lashed on to carry stuff around. I had a problem with wheel wobble. I thought a rebuild as 4 cross (instead of std 3 cross) might help. The guy in the shop where I bought the spokes noticed a cracked rim (actually both front & back). After I rebuilt the back wheel 4 cross with a new rim, the wobble was gone. Don't know if the 4 cross fixed it, as I don't know how long the rim was cracked.
I am thinking of building a cargo trailer, and am wondering if anyone has any knowledge on whether rebuilding a wheel to 4 cross for the additional stability it may bring (the old bike is long gone) is worth the effort for short trips with 50-60 lb of freight. the trailer would be attached to the rear axle, not the seat post.