Lithium & Voltage Sensitive Relay

On my 388 it was directly above the batteries.

What are you planning to replace it with, a DCDC? From what I know the 388 has the Volvo engine with the 115A Mitsubishi Alternator. As long as the cables are correct size (min 35mm2, better 50 mm2) this is perfectly fine to charge LFP. Using a DCDC is in this case a expensive way to limit charging. However, most VSRs have cut in/cut out for FLA. I'm using a Victron Cyrix Li CT in my installation (optimized for LFP). Also the Mastervolt Charge Mate Pro will do the job since it's blocking current from LFP back to FLA. 

This can be a surprisingly complex topic! As you mention DC/DC charger I assume you have an AGM starter and LiFePO4 house bank. There are two main paths.
First, alternator charges starter, DC-DC converter charges house bank. Advantage: Relatively easy to install - no (few) new cables. Disadvantage: alternator output to house bank limited by DC/DC charger, topically 50a (unless you have multiple DC/DC chargers!).

Best path: Alternator charges house bank; DC/DC charges starter. Advantage: Can take full advantage of alternator output. Disadvantage: Additional cabling, you'll need an external voltage regulator on alternator (Zeus, Wakespeed, or maybe Balmar) to prevent the LiFePO4 from overheating/destroying your alternator.