for the last 25 years we mostly do camping without hookups
we do an annual 9 day campout in the boonies with our friends: no hookups : no gennies allowed .
we do not have solar or a generator
we use a pair of Heavy duty 12 foot long jumper cables
we turn our diesel pickup around after parking the trailer
we run the trailer from the 2 rv batts and the 2 pickup batts
the pickup moves every 2 or 3 days and the pickup batts get fully recharged
as soon as we return we reconnect the jumpers
the rv batts get some equalization from the pickup batts
i have found the most critical item for voltage drop is the refer
the refer controls need good voltage , even though we are in the propane mode.
after every trip , when i store my trailer , i disconnect the rv battery cables from the rv battery . i insure that my trailer batts are fully charged when i do this.
the day before a campout i hook up 120v at home and get the rv batts fully charged
i replaced my pickup batteries with AGM batteries ; Exide Edge AGM
i have 2 of the regular RV group 27 ? batts on my trailer .
for me what has worked is jumper cables first .
Good batteries (all 4 ) second .
making sure my rv batteries are fully charged before camping and then fully charged before diconnecting them for storage after EVERY campout .