Any ideas on tie downs?

I'm thinking perhaps stainless steel for an aluminum snowmobile trailer.

Remember that the weight rating on the ring is only as good as how it's attached to the trailer. Screws don't cut it. A complete circle ring is far stronger than an S hook.
Make sure the steel won't corrode if bolted to the aluminum.

i've been using this type on my atv trailers for years. they will hold just fine if you screw them on with a self drilling sheet metal screw with big threads. just make sure you use a least a 1/4 shank screw. the ones i use are 3/8 heads and drill bit ends. just make sure when you mount them the pull will be to the side and not straight up.

http://www.ebay.com/itm/20-1-4-ROPE...item483806b6fe&vxp=mtr#ht_1518wt_670