CSX Crosstie Car

I’m trying to build a CSX crosstie car, but I need a little help. This is my first shot at scratchbuilding anything also. I was wondering if anybody knew what kind of gondola they used as a base? I’m sure that their must be a model very similar to it.

Also what would you guys use to build up the sides?

And finally how do you guys pick paint colors? As you can see from the bottom pic there are many variations.

Here are some pictures that I found on the web. I really need to scan up my own…
http://www.railpictures.net/showphotos.php?train_id=CSX%20F031