you have 2 ways to do it
in both ways you will need to install a box in wich to put the DVR with the rest of equipment
i'd recommand the DVR to have a SSD hard because is rezintent to shocks
1- put an invertor in the bus lighter and from invertor you connect the DVR and the cameras
2-it is possible without an invertor if the bus battery gives the same power as the equipment you will install ,but in this case you can power only a DVR monitor ,12 V monitor
I installed HIKVISION system on tractors using an invertor connected straight to the battery,i also connected a wifi router too for live streaming on the customer's phone
tomorrow i can put some pics maybe will help more ,english is not my first language so i just hope you can understand from my explainings