If so, how have they worked and how have they held up? How long have they been on your trailer?

 

I'm thinking of using cutting boards instead of buying the Ultimate bunk boards. I thought about mounting them right on top of treated 2X4's. Good idea?

The best idea.... do it.

How are you going to fasten them to the 2X4s?  Any mechanical fasters, such as screws, will need to be recessed so they don't dig up the bottom of the boat.

 

Countersunk flat head screws (stainless steel) would be an obvious choice.  But some plastic cutting boards can and do crack.  That would be problematic with flat head screws since the heads are wedges when tightened down.  The cutting board would also need to be thick enough to allow the use of flat head screws.

 

You'll need to do some homework regarding the cutting board materials.  Nylon cutting boards can be thick enough for recessing flat head screws.  I don't think they will have the tendency to crack as do other cutting board materials.

 

Your best bet might be to use pvc material.  It is commonly used for rub rails on boats and is available in several configurations.