I just experimented and played until I knew my own needs and could build for it, if you need any help or advise I’ll do my best to answer any questions through.
But for general tips:
If you plan on sleeping in it, try and fit in an enclosed area with no outside LoS, it can be pretty nasty to wake up to an attack from nightstalkers or other zombies that can see in the dark.
Make sure you keep a welder and some duct tape on hand, it’s generally easier to fix parts then replace them. The only vehicle type I ever build that doesn’t have a vehicle welder of some type is a motorcycle and then I’ll still keep a welder with me.
Try and keep it as narrow as possible, ramming vehicles out the way is surprisingly ineffective.
If you are going full mobile base plan the internals BEFORE you start building. This includes seating, cargo storage, vehicle mounted tools and solar arrays. You want your tools and materials all within range, if you have a team it’s even more important as you’ll probably want them to help you craft and it’s easier to train them up with books if you can position yourself to read to them all as a group. Solar arrays require a crane to mount so you’ll want to do that in the process of building if possible, not after.
If you are going full mobile base then find a tank with at least 3 working/mendable engines, you need 12 in mechanics to fit a 3rd engine so it’s much much easier to just start with them already mounted. You can strip everything off but the engines and frames and use that as the core of your vehicle, keep it in the safest area of the vehicle as you probably won’t be able to mount a replacement if one is destroyed.
If you can, doubling up your full panel walls can be helpful, you can use stowage boards for the inner walls and it means you can park at a diagonal angle without leaving gaps, otherwise always be aware that single thick walls will have gaps when you park/drive diagonally.
Water will freeze in tanks if it gets cold enough and you wont be able to get at it until it unfreezes so keep some handy in a container during winter so you can defrost it with a hotplate or something.
Armour EVERYTHING 
The heavier the vehicle the faster it will eat fuel, keep an eye on how much you have and how fast you are going through it, always carry a rubber hose with you so you can top up whenever the opportunity presents itself.
You can craft diesel and the main ingredient you can get from butchering zombies but it’s time consuming so try and avoid using it as your main method of acquiring fuel.
