Plywood Linings and Bench Seats

Just bought some ***tpart bench seats for my 92 Defender 90 (they seem a little short compared to the overall length but others I've seen are too..) and the instructions refer to slots in the tub side for locating the back BUT the rear is currently ply lined so no slots to fix to.
Any views on whether I need to take the ply out or can I fix to the ply?
Crash performance can hardly be a factor!

you're lucky you got instructions? I bought the same last year and they had none!

Think the backs are meant to fix into the tub capping

can't see any safety/strength issue though if just screwed to ply - as long as they can't come lose and whack you in the head

can't see any safety/strength issue though if just screwed to ply - as long as they can't come lose and whack you in the head[/QUOTE]

That was my guess too, I am reluctant to pull the ply and insulation off for what I suspect would be a marginal increase in strength.