A 20 ft container looks massive and less mobile that one thinks.
But you just need a truck to move it.

You can buy containers for scrap value and they last almost forever.

For deployment in summer and on events, cut a side panel and let that flap down. Weld an enforcement bracket in the length ot the flap and use a couple of inexpensive electric garagedoor winches to lower and close the flap.

An advantage of a container is that you can leave it for a longer period in an harsh environment. Just close the doors and everything inside is safe. It can also house heavier equipment than a trailer on wheels.

With the flap down plus an awning you will have an awesome outdoors makerspace, like here at the OHM festival. At the back is the FablabTruck.

But you will need light when you work inside.
A couple of roof windows is easily installed. Solar panels with led tubes too.
Standard you can leave the end doors open, but you do not want to do that in winter. So install a heater and some ventilation

Condensation is a problem in winter, so clad the inside with insulation and chipwood paneling. In the RUC container in Denmark you can clearly see the cladding.

The Fab Truck in Taiwan is not a truck, but almost a house. But still very mobile. They have six that tour schools.

In the USA you can buy or rent ready made makerspaces in a container at BetaBox. Here the inside.

Here the outside

FabLab Kaasfabriek in Alkmaar NL started with the yellow 20 ft container shown above.

They got so enthousiastic over the possibilities that they build their fixed lab out of three 40 footers. Plus one vertical as a landmark, with three 1m3 water containers with RGB lights on top. They removed and braced the inner walls.
Recently they added another two 40-footers which will give them a whopping 12 x 7 m2 workshop area op the top floor.