I had the same problem and used a small bolt and nut. BUTTTTT.. then the whole plastic bracket broke at the bottom where it attaches to the support.
The FIX...I bought an 8 ft 1"X3" board and cut it so it would go from the floor to the side of the bracket where I had put the nut and bolt. I took the nut and bolt out and ran a wood screw through the plastic bracket, the metal rail and into the 1X3 whichh was supported by the floor.
I put these in the two floor level kitchen drawers and just 2 days ago installed them in the 4 BR drawers, as two od them broke on a bumpey ride.
For my coach, the 1X3s were about 43" long for each side of the 4 BR drawers and probaly about 6" for the two Kitchen drawers. I had to take all 4 drawers out to access the back of the cabinet, but it was easy to install.
Now the drawer rail is secured into a solid 1X2 that is sitting on the floor inside the cabinet.
If this is not clear, I have pictures if someone will tell me how to post them or if anyone wants me to email them the pics just give me your address.
2001 Winnebago 37G, 2003 Saturn L300, brakebuddy Laissez les bon temps roulez