The cheapest solution I use because my needs are not as great as others :
No genny and no solar .
Instead We use a set of # 2 guage 12 foot jumpers to hook up the 2 AGM batts in our pickup to the 2 travel trailer batteries .
We park the trailer and just turn the pickup around .
The pickup gets driven every 2nd or 3rd day .
We hook up all 4 batteries as soon as we return .
The 4 batts equalize .
We dry camp . We do a 9 day boondock every summer since 1984 .
Our setup has worked well for over a decade .
This works good . no genny . no solar .
For heavy current draw I consider Roy B to be the expert .
For heavy duty needs RoyB says two 6 volt GC2 golf cart batteries are the only answer .
i replaced my duramax pickup batts with Exide Edge AGM group 78 for $ 140 each from BiMart .
Like my Pop said " There is no substitute for cubic inches " .
That includes batteries .
Do a Wikipedia about AGM batteries and you will find the reason we made that switch .
Over time we have converted to AGM in our cars,truck, boat, and TT .