All of my camping trips are based on PLAN Bs....
If I was to use my Truck Start Battery like having a 12V COOLER connected and run down the battery I would then start up my 2KW Honda EU2000i generator that is sitting secured and covered in the tailgate corner of my truck bed. Then I would hook up my portable BATTERY CHARGER and charge up up my truck start battery to start my truck.
My battery situation however is geared for camping off grid and consist of two groups of two 6VDC Batteries in series and has a great long term use when camping off-grid... What you are describing would never be a problem for us camping off grid...
This was my original BATTERY BANK setup using three each 12VDC Batteries in parallel... This has recently been replaced with a new 12V battery bank that consists of two groups of two 6VDC Batteries in series.
The new battery bank is installed in this battery box that has a slide off top lid. This is sitting on the trailer tongue area replacing the three 12V Batteries originally used... This battery box extends out on both sides of the tongue area and fits perfect inside the the two welded on mounting rails. I also have a second 10WATT Solar panel so that each 12V groups will have a trickle charge using the two 10 WATT small solar panels when sitting in the high sun..
This is my 2KW Generator sitting inside my covered truck bed.. This is pulled out onto the dropped tailgate when being used... ALways having the generator mounted in my truck has been used many many times getting someone else truck's started. Also being secured in my covered and locked truck bed my generator goes where I go..
Its all about PLAN Bs hehe...
Roy Ken