David,
Can't a heavier wire to the battery help avoid the voltage drop easier?
Like OO welding cable?

Just thinking of an easier, less expensive solution.
I used to add this type of set up on all my GM stuff, with excellent
results.

Later,

            ______________
           |[  ] [  ] [ ]\
           |    |    |    |
     ~~~ ~||-(())----(())-|

Terry--
74 Campmobile- (Clementine)
85 GL- (Delilah)
86 BMW 325 ES- (Eva)