I hae a little 6' x 4' Ifor williams trailer, the only problem I have with it is that it's relatively shallow, especially when it comes to piling garden cuttings in it. I've decided to build some side extensions for it to make it more useful. It already has mounting points for them, the front has a socket to slip some box section in with a captive bolt so you can bolt through it. The back has a plate with a hole. I was thinking of using something along the lines of 30mmx30mm x 3mm angle for the frames infilled with 10mm marine ply. The back would be the same but hinged at the top with a simple plate and bolt through the side frame as the hinge. Some over centre catches to hold it shut and then maybe a hasp and staple to lock the two tailgates together. I initially thought of using box section rather than angle but couldn't work out an easy way to attach the ply. I want to use Ply rather than weld mesh as I may make a proper lid for it later to make it into a proper box. I know Ifor Williams sell sides but at nearly three hundred quid I'm sure I can make these cheaper. Does anyone have any suggestions, hints tips etc? Would I need to add a triangular brace to reinforce the sides or will the ply do this satisfactorily. I don't want to make them too heavy!