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profdant139's avatar
profdant139
Explorer II
Jan 24, 2019

Underbelly project: coroplast on the bottom or metal?

I am finally getting close to getting started on my underbelly enclosure project -- many family medical issues (mostly resolved) have gotten in the way.

My trailer does have some fiberglass insulation, covered by a thick black plastic tarp-like material, but I am going to add extra insulation below that barrier. (Since my trailer is raised up several inches, I have plenty of room to add more insulation without affecting clearance very much.)

I have all of the framing materials I need -- aluminum C channel to support things, and bars and strapping for additional cross support. I am planning to use thick solid extruded polystyrene (XPS) for the insulation. From what I have read, it has the best R value per inch, and it is not affected by moisture.

I don't think I can leave the foam exposed to road hazards, since it is so brittle. Most folks use coroplast (corrugated plastic) as the bottom layer.

So here is my question: how does coroplast hold up over time? It is not very strong -- doesn't it get damaged by gravel thrown up by the tires? (We do a lot of gravel road towing, at slow speeds.)

Is thicker coroplast sturdier? It comes in a variety of thicknesses.

Instead of plastic, does anyone use either aluminum or galvanized steel sheeting on the bottom? That would be much sturdier but also much harder to work with.

Thanks in advance for your advice!
  • Don't over think it. Use the CP. It is easier to work with, cheaper to buy, probably lighter, and easily replaced if it were to get damaged. It is very tough stuff though, so I think it will take a pretty significant impact to do anything other than dent the outer layer.
  • I have cut into mine to add tank heaters and can tell you it's pretty tough/durable stuff. My camper is 13 YO and the stuff it not brittle in any way and has no holes in except the ones the factory and myself put in it.

    I would not replace it for metal.
  • Scott, that's great info -- no way the rest of my trailer will last another 13 years! Thanks.
  • profdant139 wrote:
    I can't believe that I did it again -- posted in the wrong forum. Moderator, I am ashamed. There is no other word. This belongs in Modifications.

    I have to learn to re-check to make sure I am in the right forum before starting a thread. There is just no excuse for this. It's not as though I am a newbie, for heaven's sake.

    If I knew how to post an embarrassed emoji, I would.


    Live & learn. Move on. Don't sweat the small stuff.
  • No problems after three years with this TT and I do dirt roads.

    Hey! Lighten up on yourself. Your posts are interesting wherever they appear.
  • Coroplast is quite tough, it is also light weight and easy to work. I would never consider galvanized, have you ever seen a piece of old galvanized sheet that wasn't rusty? Aluminum might work but it would be a lot more expensive. And no better IMO.
  • The CP held up great for the 13 years I had our last TT. I think it's tough stuff.
  • I can't believe that I did it again -- posted in the wrong forum. Moderator, I am ashamed. There is no other word. This belongs in Modifications.

    I have to learn to re-check to make sure I am in the right forum before starting a thread. There is just no excuse for this. It's not as though I am a newbie, for heaven's sake.

    If I knew how to post an embarrassed emoji, I would.