I am installing a Multiplus inverter charger in my motorhome, it will be in the back under the bed, the lithium batteries are under the entry steps in the middle of the coach. I know i have to run large cable for such a long run(20ish feet). But my question is if i run the two (4/0awg) battery cables needed to the DC+, can i run a shorter set of cables from Multiplus DC- to the motorhome frame(just under it) and then up size my DC- to frame cable on the batteries where they are already hooked to the frame. essentially using the frame of the RV in place of the DC- cable. This is mainly to save in installation cost. Is there any issues this would cause. thanks