Steel is expensive here in cali, and the tools to work with it can be spendy ($20ish for a single metal drill bit at Home Depot  ). I don't have anything I can cut it with... or weld  :'(

So, if plastic is lighter, easier to work with, and I can use my existing wood-working tools / cutters / bits, it may be a more economical solution. I'll have to re-price steel (been a year or so) and the plastic. I still want to build my own square-tube bumpers with class 3 hitch front & rear... so I guess investing in metal tools isn't TOO bad of an idea...

Here is why you need a front skid p[late.

93, 8 Valve 3 Speed

Have you considered oil changes? You might want to cut out some holes for oil to drain and to get the filter off!

The plastic is a viable option. Four Wheeler Magazine once built up a 2003 Lexus GX470 (fancy 4Runner) to run the Rubicon trail and they used some sort of plastic material to cover the bottom. It would work, and it's not the worst idea because plastic doesn't rust, unlike steel, and it is much cheaper than 1/4" aluminum.

My buddy back in Colorado runs a Toyota in a big Yota club and they do some aggresive crawling.  Almost every one uses the high density molecular plastic and it holds up just fine I was suprised to hear.

U.H.M.W. seems the best option, IF available AND affordable. I checked out a plastic supplier and it can be obtained in many dimensions. A 4X8  1/2 inch thick was well over $100. My 1/8 inch thick steel plate was 25 cents/lb. so thats $12.50 for a large 50# piece. Like I said earlier, if only we could get that cost down... I'm still sending out feelers for a better source. Maybe "Trackin_Tracker 33"s  dad can get us all a good deal !  'Till then, it's steel. Same reason my cage and guards are DOM and ERW, not Chromoly, affordability and availability.

I took some rough measurements...

"Big belly pan" protect from cross-member to transfer case bracket and frame to frame: 32" x 32"
"Small belly pan" protect from cross-member to transfer case bracket by width of braces: 32" x 16"
To Protect from croos-member to front (to protect diff): 21" x 21"

*edit: to clairify, big belly pan and small belly pan are covering the same area. But, one is wider (thus protecting everything between the frames), and one is narrower (exposing the exhaust system).

The under-belly sheets could be easily made & attached leaving everything flat. But I'm concerned about going from frame-to-frame with a big belly pan. It would put the plastic right next to (and possibly in-contact-with) the cat & exhaust. UHMW is only rated up to 280F, and constant temp operating temp of 180F http://www.jjorly.com/uhmw_technical_data_sheet.htm.

A narrower under-belly (32" x 16") would leave the exhaust exposed to rocks, but away from the plastic. And it would be cheaper for material.

A front skid (to protect diff) looks much more tricky. I don't see a flat area to bolt to up to around the bumper, and even taping into the cross-member looks out of my fab skills (self-tap screws / bolts maybe? Would that handle abuse?). Might be able to use the bolts where the lower A-arms are, but that will require some heating and bending:
http://www.garlandmfg.com/plastics/heatformingparts.html

Ideally, I would think it best to have some kind of heating "rod" that the material could be bent over / around - where the heat is localized to the area desired to bend. Anyone have any ideas?

UHMW vs HDPE

I can't find a side by side by side comparison of the two for heat, UV and impact resistance or weight difference. But, the price difference is huge.

Anecdotally, HDPE seems to be softer than UHMW (more expensive, but takes quite a beating).

Bending the two materials seems to be about the same procedure (heat & bend), but I'm not sure. Still researching this.

UHMW Costs:
Wow, yeah. Looks like a 1/2" x 24" x 48" sheet is about $100 |removethispart|@ IND plastic & McMaster
http://www.indplastic.com/index.cfm?fuseaction=detail&id=858932&product=463
http://www.interstateplastics.com/detail.aspx?ID=HDPEcuttingboard-SN051
http://www.mcmaster.com/:
Interesting to note: 1/2" x 24" x 48" = $80 (VHMW = UV resistant) (McMaster Part #: 8769K72)

HDPE costs are about 1/2 as much as UHMW
1/2" x 24" x 48" = $50

Costs for HDPE, double the cost for UHMW:
Big belly pan: $100
Small belly pan: $40
Front skid: $25

On a side note: Material appears to be available in black (UHMW) for about 10% more. I've read that UHMW has low UV resistance, and is not ideal for outdoor applications. Will this be a problem being under the trucks?

4x4 mech by my house says plasic or metal doesnt matter itll cause too much heat to go in the wrong direction causing more probs than benifits if i put holes in for venting that will take away from the "slide effect" im thinking seperate skids.............Im sooooo confused. 3 pieces not 1 seems more better

Einstein once said "never memorize anything you can refer to", when I have questions about plastic , I'm gonna refer to Jeremiah! This is getting like the "tube vs. pipe" debate. Lotsa engineering and research here, and all excellent stuff! Lemme know what you guys decide on. K.I.S.S. principle, gentlemen. This ain't the space shuttle. Speaking of space shuttles, a modular design would seem better on consumable parts like belly pans, that way I could replace only that area thats busted-up instead of the whole pan.

Here is an old pic of Hagens skid