wow... you guys over think this stuff.... 90% of the time a receiver hitch will have a rating much higher than the payload of the vehicle... like my pickup, has an 1600lb payload, meaning, the factory doesn't recommend me carry more than 1600lbs on the rear axle.. my receiver hitch itself is "rated" for 2000lbs... meaning the hitch is rated for more than the springs are, this is how most are set up... for you to say a receiver is rated for 500 is funny to me, as most hitch inserts are rated 2000-5000(for a good one)... i have an adjustable one that is rated for 500lbs, funny thing is I pull a car trailer with it all the time.. I've ran a skidsteer to the front of the trailer so far that it was completely in front of the trailer axle(placing 2500-3000lbs on that hitch that's rated for 500lbs)... driving with it like that, of course not, but if you're 300lb ski is going to create 2000lbs of force when hitting a bump you're tires would blow out from the weight of the vehicle every time you hit a bump... as far as having issues with a unibody vehicle, as long as your hitch bolts to the rail from the bottom and the side you'll be fine, unibody is stronger than most people think, if the right equipment is used(i own a body shop, i deal with them all the time), and I've seen just as many problems with hitches on full frames as i have on unibody, it's all in proper equipment... seems like people just need to read less warning labels and acquire more experience...
my point being... your receiver won't be the part that fails... it will be the carrier instead, make sure your main bar will be plenty strong as stated 2x2 1/4" wall me personally would do 3/8" wall... also... strap the ski to the carrier, and run a safety chain to the hitch, just for safe keeping if in the slight chance something would go wrong, it's still attached and won't hit the ditch and tumble or slide into the other lane... do this and check your payload rating(I'm guessing it will be over 500lbs) and mind you, this rating is not a "static weight" rating, so if it says it will hold 500lbs it means it will hold 500lbs, not 300lbs after you factor in the force of bumps, it's tested to withstand the abuse of 500lbs...