my personal, honest and limited knowledge of these

DC to DC is an expensive rort

both your Alt and DC to DC will fully charge a battery

Alt will charge it at 75-140A depending on your Alt
and yes they seem to charge BOTH batteries without blowing them up of stuffing them up

DC to DC will only charge at 5-10A (the big "40A" DC to DC have not hit the market completely and are very expensive)
with DC to DC you are using your 2nd (or main) battery to charge the Camper one as well.......but over a longer period........
(yes they have Solar input on the regulator - but if you buy Solar they have the regulator as well......)
so
what is the point of having a DC to DC to charge 1 battery off another battery - when the Alt in your car does it any way


I would put a decent sized cable from your 2nd battery to an Anderson plug at the rear
depending on the size of your Camper battery, put an appropriate sized fuse at the 2nd battery end

save yourself about $200

it works for me, and my battery in my Van is always charged
and running lights and engle only, I get about 4 days before the battery is really needing a charge