A lot of folks cross the line from potting soil and those processes that support containers to soil based concepts like manure. The internet advice usually does not point out the context that makes the different methods useful in the different situations.
Raised bed is much more akin to potted plant maintenance than soil gardening, and aeration, drainage and adding available nutrients follow a slightly different reasoning. If the beds are open bottom, then farming techniques for hill row planting work well as the access to the fungal hyphae network in the soil is then allowed.
That bottom and whether it exists or not will greatly influence your successful support techniques. Something is working, since plants are growing. You seem to have in mind that they are effectively pots when you mention "polysterene balls". Also your "trough" description points me that direction. I assume they are pots in effect.
You might consider leaf mold and hardwood bark mulching rather than manure. Organic fertilizers rather than basic amendments that require further breakdown might be the better path for a potted plant. @Meadowlark
has some fun with hugelkulture in pots, which points to the use of wood as as amendment. The bark and leaf suggestions I made are a shortcut to that goodness.