Your bumper is rated for 100 lbs. I'm not sure how the ratings were determined, but IMO, they are too much.
I really don't know the weight of a spare tire/carrier, but the rotational force caused by that tire/carrier bobbing up and down on the road really is too much for it already with no other attachments. I've heard of and personally experienced the damage the tire can do to the bumper.
The best way to prevent the tire from tearing off the weld joints is to put it as close to one bumper mount on a side as possible.
2007 T-286SR Cherry/Granola, #6236, original owner, current mileage: 9467.8 (as of 5/26/19)
1997 T-2653 Blue Denim, #5471
1979 12 1/2' MC, Beige & Avocado, #4639
Past Sunlines: '97 T-2653 #5089, '94 T-2251, '86 T-1550, '94 T-2363, '98 T-270SR