Tear in black undercoating - repair help needed

I inspected our RPod this weekend after a trip and found a small tear in the black undercoating near the driver-side rear stabilizer jack. The tear is a few inches long and I am wondering what the best method would be to repair the tear? Has anyone had to repair this undercoating before?

I'd be inclined to try Eternabond roof sealant tape.  That stuff is durable and waterproof.  The glue is really sticky and stays so for longer than you'd probably own the trailer.  The key to getting it to stick is having a clean surface, free of dirt, crud, and solvent or detergent residue.  

Thanks all. I used some Gorilla brand waterproof patch & seal tape last year on a tarp for an outdoor skating rink. It worked great. It sounds like I can use the same product on the under side to seal the small tear. Next time I make it up to Anchorage I will look for eternabond at a few box stores. 

I used Flex Seal, both the spray and the brush on. I went over whole bottom and filled every hole I could find. I have drilled holes in bottom and repaired damage in several places.