You shouldn't need a fuse between the camper battery and the fuse bloc; it is, of course, full of fuses! A kill switch is a reasonable option.
What kind of truck are you using? If your charging system runs at 14v or more, you will get MUCH better performance, i.e. a faster charge, out of a properly sized relay based system, either key controlled or automatic.
If you must use a D250S, then add the SmartPass, otherwise you are limiting your charge to only 20A or less. Lifelines like a charge rate of up to 5C, not the more common C/5.
The combination of the D250S and a SmartPass is expensive, but it does include a solar controller at no extra cost and it does assure a high charge voltage during the low amp absorb stage. (Just costs a lot of money and takes up a lot of space.)