Fuses at both ends, and wiring suitable to the fuse size, 20 amp fuse 12gauge wire , this will be ok for a toad battery maintenance charge, however if you hook up and the toad battery is dead, you will blow the fuses.
If your charging to maintain because of a toad braking system draw, you may need larger fuses and wiring depending on that draw, you would want to double it.
Brake system draw 12 amps , charge system fuses 25 amps & 10 gauge wire , for example.
99DSDP 3884, Freightliner, XC, CAT 3126B, 300 HP /ALLISON 3060
2000 Caravan toad, Remco & Blue Ox.