GRP rear tub - a bit too wide...?

[jps]

Last night I finally got round to offering up the Equinox rear tub that I bought 14 months ago....

It was only a very rough placing of the panel over the frame - but it seems to be coming up slightly on the wide side. I measured the chassis width - and it is bang on the book spec. I didn't measure the GRP precisely - but would estimate that the GRP panel is about 8-10mm over width altogether - so overhanging the metalwork by about 4-5mm each side.

First thought is that I space out the side panels an equivalent amount (assuming I have enough material on them to do so) - to maintain a 'straight side' to the bodywork.

Or do I need to look at another solution?