CA,
Unless your son has a pair welding cable between the 8955 and the bank, that is where he is loosing. None of the converters (afaik)are remote sensing. That means that the 0.6~0.8V that he looses in line loss is killing his charge rate. He can either more the converter closer to the bank or invest in some gunga-moma cable.
The entire life of a 12V battery is between 12.6 and 12.0, so loosing that 0.6V on the way is a killer for recovery time.
We did a lot of boat work before the depression, and this was a problem that the performance cruisers (read retired racing sloops) faced constantly.
Matt