Retail Shop Roller Shutters
All of this is based on the premise that you have "standard" zombies incapable of climbing.
Retail Shop Roller Shutters are strong, compactable, and easy to deploy. You can get them from any mall or mechanic's shop in a variety of heights and lengths and styles. I wouldn't want more than 10-15ft long ones mostly because of the potential for uneven ground leaving significant gaps, but that depends on how smart your Zs are! I think the most effective would be ones with holes so you could stab through to kill Zs if you end up with too large a following, but solid metal ones would do the trick about as well.
The idea is these collapse upward into a solid rectangular box. Have a couple of these on the roof of your forts. When you've found a suitable site, extend from the lead vehicle backward and the following vehicle secures it. Then drop! You could build a triangular palisade this way with your survivors neatly out of harm's way for the whole setup process. You could build a fort with sufficient interior space using six vehicles, but it would be easy to expand that number if needed or contract it down to a minimum of 2 vehicles (if things go badly for your survivors or you have to split the party). Generally speaking I think you'd have eight vehicles as part of your wall and two inside. If we're talking 20ft long vehicles with 15ft long shutters that means (pray for me I'm bad at math) you have an interior space of something just under 3000 sqft, with about (assuming your vehicles are 10ft/20ft) 1000sqft of that space taken up by your inside vehicles. Not bad at all!
Once you've gotten the fort set up (completely out of Zombie range if you need to) you can decamp and kill anything in your fort. Then you can anchor the rollers with additional spikes/whatever to ensure nothing lifts them up in the night (or better yet, build a lock into the top of the shutter), with tripwires hung with bells a few inches behind the bottoms of the shutters to alert you in case they're pushed back too far by weight of bodies or something tries to dig underneath!
If you want to be doubly secure (you're planning on a multi-day stop, standard overnight practice if you have to camp at a high-Z spot, what have you) you could have an inner and outer fence. Just double the amount of shutter "booms" on your vehicles. In that case the outer fence should certainly be made up of shutters with gaps so your guards can stab outwards. Guards would normally be posted on top of the (presumably more than 8ft tall) vehicles, probably just 2-3 given your total number of survivors. They could use ladders to get down in between double-walled sections of perimeter if they need to. Simple cloth "blinds" could be set up on top of your vehicles to allow your guards to stand watch while not being seen by Zs.
The remaining two vehicles would be parked side-by-side in the center of the encampment. These would function as your sleeping quarters, with survivors sleeping inside and on top of the vehicles for maximum security.
Metal skirts would also need to be deployed on your vehicles to stop things slipping under them at night, and the passenger sides would need to be relatively free of entry points (no windows someone could crawl through, etc). Shutters could also work here, with interior latches so they could be deployed from inside the vehicle.
Always choose a campsite with maximum open space around it to ensure that you can spot zombies from as far away as possible. With about 2,000sqft to work with most days you could easily have enough space for everything that has to happen outside of your two inner fort vehicles. Even the loss of two vehicles would still give you about 1,000sqft of working area once the inner vehicles are accounted for. So not bad!
Additionally, these would be pretty easy to pack up in a hurry. If a section got breached and everyone fled back to the vehicles they could be retracted and moved into traveling mode from inside the vehicles themselves. If you picked the right shutters the rectangular boxes would even be solid enough to walk on, so even if a neighboring vehicle was overrun someone could balance-beam across, unlatch, and get back to the working ride!