I was able to do a little research to find the factory tire was a 5.90-12. The KR25 options come with a wheel, but if you just want the tire the Kenda Karrier S-Trail ST145/R12 Radial Trailer Tire - Load Range E # AM10140 will work well for you.
If you are looking to replace the wheel as well, you could use the Aluminum Lynx Trailer Wheel - 12" x 4" Rim - 5 on 4-1/2 - Silver # LH45FR and have them mounted at a local shop. Or we have the tire and wheel combo, but the wheel is galvanized... view full answer...
A 145/80-12 Load Range D radial tire like # AM10130 carries a 1220 lb per tire/2440 lb per axle capacity which will handle the weight of an 1800 lb trailer with no problem.
I've linked to a product video for the # AM10130 tire. view full answer...
Unless the bumper is reinforced and has a stated weight capacity I do not recommend putting any attachments on it. Most factory bumpers don't come with enough weight capacity to hold a bike rack and bike so most campers end up needing to install a new receiver hitch. To know what size you'll need you'll have to measure the distance on the inside between the I-beams of the frame.
If you have a frame distance of 22"-72" I recommend the Adjustable Width Trailer Hitch Receiver for RVs Item... view full answer...