I am going to use 1/2" MDF for a CB-70 rack, 11 tall. I know the stuff can sag like crazy, but at only 18" wide I don't think it will come into play. I could only find one rack using MDF:

http://www.reptileradio.net/reptileradio/showthread.php?t=4069

and it's too short to be picked up on the search.

Anyone built a rack using MDF that can give feedback on it's suitability?

I have never had good look with it personally. One spill of water anywhere on it and you can hang it up.

Can't give you much experience as far as rack building goes, but I've built my share of speaker boxes with it. Make sure you seal it really good, the stuff is like a sponge if you get it wet. It will probably take a few coats because of how well it soaks up moisture. Also, you may want to route out slots in the sides to give the shelves a little more strength rather than relying on the strength of the glue holding the MDF together if you just use screws on a flat joint. Is there any reason you're going with the MDF?

Can't give you much experience as far as rack building goes, but I've built my share of speaker boxes with it. Make sure you seal it really good, the stuff is like a sponge if you get it wet. It will probably take a few coats because of how well it soaks up moisture. Also, you may want to route out slots in the sides to give the shelves a little more strength rather than relying on the strength of the glue holding the MDF together if you just use screws on a flat joint. Is there any reason you're going with the MDF?

Yeah, I've built with it before too, just nothing humid/warm like a rack. Was planning to seal it well with spar poly. Screw and poly glue construction. I was thinking MDF for ease of construction and expense. Don't have to dress edges like plywood or melamine.

My dad fillets fish on a scrap of MDF that was sealed, I'm shocked how well it held up with use and thought it would work well if it held it's shape it's not too heavy, cheap etc.

Without sealing it I know it would ruin pretty fast. It reminds me of posterboard on steroids.

Sounds like you know what you're doing, I expect it would work out just fine. I was thinking about using it myself at one point, but didn't really want to go through the trouble of sealing it.

I still remember a large breeder had his racks made of mdf. Than one of the shelves had a scratch and it got some water in it . it Swelled so much he had to cut the snake out of the rack. He went to plastic racks after that.