I also have my motorhome covered through National Interstate. They've been fine to deal with administratively, but I've never had to file a claim. I purchased my service contract through Wholesale Warranties.
If you search on the forum for "extended warranty" or "service contract", you'll find lots of discussion that will probably answer most of your questions. Good Luck!
John & Diane, Fulltimers. RVM103 NHSO
On the road since June '12 with Lincoln, the guard cat.
2002 Dutch Star 40, Freightliner, Cat 3126, 2004 Element