Elvin,
Hi, I am not sure if you resolved your question already - looks like you posted it almost a month ago. I just wanted to say that I made a larger cutlery drawer for my little trailer and replaced the slides as well. I added custom sized 2x4s that were fastened to the centre cabinet divider and the outer
fiberglass cabinet wall. If you would like, I have posted a brief description and some pics (starting post 67 page 5) in my rebuild thread.
The screws that went through the
fiberglass wall to the 2x4 had very large flat washers on them to help distribute some of the flexing I anticipated. I think I also used construction glue to help the mechanical fasteners. I also ended up making an almost complete box out of plywood for the box to slide into
Hope you find a solution and look forward to following your progress.
Jay