The truck cap it's self is very flexible so I reinforced it around the "A" and "B" post with 40x40x3 RSA.
The extra steel on the "A" post enabled me to fit a cross member to support the steering column.
I also fitted some extra steel around the back of the cab.
The O/S/F door also got some steel reinforcing .
I was a little worried the steel would twist the door out of shape but all seems to be OK when the door was placed in it's hole.
I might leave the fixing blots and screws around the "A" and "B" post in place