I'm planning my 12v build out in my 4R. I plan on utilizing a D250s, dual batteries under the hood, 1 100w solar panel mounted full time to the roof rack and a CTEK shore charger. This fall I hope to tie the system into a Conqueror 490 extreme trailer using a rear Anderson plug. I'm using the B2B since I don't think the 4R puts out high enough voltage to properly charge AGM batteries. However, I'm still not crystal clear when a Smartpass is needed. Can anyone shed some light on this? Anyone use the D250s/Smartpass combo?