Nick 

Did you ever consider using a relay and running the pump off your 24v system? That is assuming it can handle 26-28v.

Presumably when you're running AC you're either plugged in, so your chargers are on or if you're running on inverter, it is, if anything, more efficient to run directly off the batteries vs. through the inverter.

Just a thought.

--
Scott 
2007 A54 #69
SV Tengah
http://www.svtengah.com