If you watch teardowns of ready built batteries on you tube that are using large prismatic cells, you will see that compression is not used, at the best the cells will be taped together.
I suggest installing with insulating material between cells and the metal and aiming for a 'snug' fit with the cells at around 50% SOC. High density closed cell foam or neoprene could be used.
Good discussion here,
I assemble similar to the picture below with high density foam sheet on each end plate ( metal or thick ply). The cells are held under slight restraining force whilst the side plates/ply are fixed in position.
View attachment 68412
To overcome any issues with buss bars I use flexile braid.
View attachment 68413
I see you are in the UK,
high density foam sheet available on ebay , various thickness including adhesive backed .
Must be closed cell to avoid moisture issues.
high density foam
To isolate between cells use high temp baking sheet,
Bake-O-Glide STD0450 Non Stick Reusable Cooking/Baking Liner Roll, Brown, 1 m x 450 mm: Bake-O-Glide STD0450 Non Stick Reusable Cooking/Baking Liner Roll, Brown, 1 m x 450 mm: Amazon.co.uk: Home & Kitchen
www.amazon.co.uk
Mike