I have a PT185 and mounted the spare on the right side of the trailer. I don't remember what brand it was but I got it at Walmart a while back. Its a round piece of tubing about an 1 1/2 in dia. formed to a 90 deg. angle. I have plenty of tire to boat clearance because it offsets the tire about 4 or 5" from the trailer frame. I mounted it on the right side just behind the front most cross brace on the trailer. At least I think thats where it is. I would go look but the boat is still in storage. Hope this helps.
Carl