Hi stan.nations,
When I ordered mine from Lippert, they warned me that it would void the 1 year frame warranty. Their explanation was that they'd have no way of knowing whether I used the receiver for a bike rack, or to tow a heavy vehicle (maybe they were thinking of space shuttles
). I pushed back a little and asked if the hitch they designed would actually work ok with the frame and brackets they designed, if I just used it with 2 bikes. They agreed that should be no problem using the receiver in that way.
Lots of owners have bolted on or welded on receiver hitches without causing frame damage. But the underlying issue is that if you had a problem of some kind that was traced back to the frame, their warning makes us concerned that Lippert might try to refuse the warranty claim, using the modification as an excuse.
There was another thread a few months ago discussing these warnings about voiding the warranty. The essence of that discussion was that they might have to prove that your modification caused the damage in order to actually deny a warranty claim.
Here's a link to additional general info on warranties.
Btw, there are other choices; some owners have mounted bike racks to their pin boxes.