When using a lead-acid pack, I found an external lead-acid charger arrangement worked for me. However, the new lithium battery charger is larger, more expensive and has a really wimpy data cable that would quickly be destroyed through repeated connects and disconnects. So, I've decided to find a way to mount the charger so it does not need to be removed for each journey. To the left, you can see the end result. The charger has sufficient ventilation to keep cool. It also allows inspection of it's indicator LEDs on the end of it.
To the right is an image of how the holder just before it was installed. To mount, it's bolted in with nylocks and washers to the fiberglass battery pan structure. If assembled correctly, the charger should just "snap" into place. The only cable modification I needed to do was to lengthen the battery charger data cable so it could reach the "LIN hub". I suspect a "new" BMS system would only provide connectors & cable without being assembled, providing an opportunity to make cable lengths correct the first time.
Parts & tools required:
6ft piece of angle iron (you'll have some left over)
an angle iron bender (or use a vise & hammer)
tape measure or ruler
(10) 6-32 flat head screws with matching Nylock nuts
(4) washers - used for mounting to the Plexiglas battery tray
spray paint and primer
zipties (to run data and power cable to battery tray)