We are only allowed 16' x 8' tunnels now since the new head of Council Allotments took over.
Here is a picture of how I laid out the inside of our 30' x 14' ( as I remember) communal tunnel, which is shared by about 8 people.
I used to have three of the beds but gave them up last January to people on the site that didn't have a greenhouse.
If I were having a tunnel myself, this is how I would lay out as it lends itself to a good 'Rotation Plan' situation, plus it is quite easy to tend the beds without walking on them.
PS Just thought you might be interested for when you lay out the inside of your new tunnel