Maybe some of the Flex seal stuff they are selling on TV. Seems to do a good job.

If you can find the leak, and it is a crack, you could try melting the material back together with a soldering gun.  They make a heat gun kit for fixing plastic and urethane parts for cars and the fenders on ATV's, but the kit with the gun is not cheap.  Might check with an auto paint supply store and see if they know of a shop in your area with one,or check with an ATV dealer, they might have one and would try for a few bucks if you find the leaks first.

 

Spray on or sealers would be a temp fix if the leaks are on the bottom and you are dragging them on the ground and rocks.  Would think it wuld get ripped/worn off pretty quick.

For skid plate, might think about some "Formica" or other countertop laminate pieces and epoxy on the bottm.  If that is where your leaks are, that might be the fix there as well.  Check with local floor covering stores to see what they might have on hand is scrap pieces. 

That's what I was thinking. I live beside and still do occasional work for the woodworking shop I retired from last year.  I'm still able to use my old workspace, that's where I built my highbanker.  They have plenty of laminate scraps to choose from.