Have a look at the UKcamping web site for details of
The Wingfield Arms Campsite, Montford Bridge, Shrewsbury......they do take long termers, but not sure of the time limit , if there is one. Its about 5 miles out of town.
Also, in the winter period you can get up to 3 months seasonal pitches at Oxon Hall Campsite.
We have over wintered there in the past. It has a park and ride next door plus local shops and excellent facilities.