Warranty?
Don't have an answer on the warranty. But here's what I found when I had the same questions re putting a hitch on my '04 3 hatch.
- I could buy a hitch from a dealer in Canada
- Mazda UK shows a hitch on their web site for a 3, and gives a table of
allowable trailer weights, depending on whether the trailer has brakes
and the maximum expected grade that the car+trailer will be driven
on. Those weights were all in excess of 2000 pounds.
- when I looked at the .pdf install manuals on-line for the various US
hitch purveyors, like Hidden Hitch and DrawTite, they all started
basically the same, something like "using the existing holes in the
body" - yup, the 3 body comes from the factory with holes for
mounting a hitch. I can't say that's true for an '08, but it is for
'04 and several later years.
Bottom line, the bloody lawyers wrote the US manual and are afraid we'll
all kill ourselves and sue them if they allow us to put a hitch on the poor
little baby.
We pull a Coleman Taos popup camper with our 3, have put over 18,000
miles on the pair in the last three years, including runs through the
Rockies with mountain passes over 10000 feet. No probs, but you can't
be afraid to shift and let the engine stay in it's power zone. Trailer
weighs about 1300 pounds when we pull it.
If you want to check our hitch prices, try
www.etrailer.com
Sorry I can't tell you if your warranty would be at risk.
Glenn