You want to get the DC-DC as close to the leisure battery as possible. I think the manual even suggests a maximum. The reason is there will be a voltage drop between the DC-DC and leisure battery that the charger knows nothing about. It will happily (within limits) work with a lower voltage at its input so better to site the DC-DC at the back with the leisure battery.
Lithium will happily take as much current as you can supply, so I would go for the 30A version, or even the new Victron XS if your budget allows.
Go for fuses (as recommended in the Victron manual) in preference to circuit breakers, unless you opt for the quality breakers rather than the cheap ebay or amazon lookalikes.

 

Thank you so much. That makes sense.
Are 16mm2 cables what I need?

 

Thank you so much. That makes sense.
Are 16mm2 cables what I need?

Yes if using the TR-smart. I think the XS can take up to 25mm2 so you could go bigger if you're using that.
Might need something bigger from the leisure battery if you are wanting to add an inverter though

 

Thanks again. I need to put my shopping list together and try to figure out how to route the cables. There are cables fitted already however they were installed when my van was fitted out. I think this will be the hardest part of the job other than my bank balance taking a hit.

 

I am looking at fitting a 100a lithium ion battery.
May go solar later on.

If you are thinking solar I can't really see the point of fitting DC DC

Your solar will happily keep you topped up with a big enough panel.

Better spending your money on solar now IMHO.

I have a 100ah lithium fed from a 200w Renogy panel on the pop top via a Victron MPPT

Never found the need for any sort of a split charge system. Solar is great.

 

Thanks Orion. I am new to this stuff. We are preparing our van for retirement, so I will see how things go. I am sure there is a good second hand market for DC to DC chargers should we decide to go solar.