Using 120 volts for charging over longer distances has distinct advantages. There are conversion losses converting 12 volt alternator output to 120 volts and from 120 volts back to house battery charging voltage.
Charging 12 volt batteries is especially sensitive to line loss. Using short heavy cable with as few connectors as possible is important.
However, line losses are much less at 120 volts.
A 1000 watt 12 volt circuit requires much heavier cable and fewer connectors. 12 volt resistance loss at some point exceeds 120 volt conversion losses.
1000 w @ 12 volts = 84 amps and needs extremely heavy 6 gauge cable.
1000 w @ 120 volts = 8.4 amps and easily works in 14 gauge lamp cord.
500 w @ 12 volts = 42 amps and needs 8 gauge cable
500 w @ 120 volts = 4.2 amps and can use any cheap extension cord.
120 volts AC for battery charging is no more dangerous than an 120 volt electric hedge trimmer or lawn mower.
I wish you good luck and happy trails ahead.