Would having the drive in a large tub be better than muffs on the hose?
That will destroy your impeller unless the tub is deep enough to put the water level at or above the level of the pump inside.
When the boat is sitting in the water, the level is such that it will put the water line somewhat above the level of the pump, such that if you were to remove the pump inlet hose, water would "siphon" out and into the bilge.
The pump if dry, will NOT suck water from the drive to the pump unless the entire hose from the drive to the pump is "primed" with water, and there's water IN the pump.
Otherwise, if you want to operate the engine on the trailer, either connect a water supply hose directly to the pump inlet, or connect a flush adapter (muffs) to the drive.
Also, if you suspect there was a previous disintegration (or disintegrations) , you should remove the hose to the oil cooler (both sides) and backflush to remove previous pump disintegration fragments. I actually had to use needle-nose pliers to extract the fragments from the inlet side of my oil cooler. Backflushing with 70 PSI water wouldn't budge them at all!