Sorry, I have no pictures of potted roses but can help you.
Long term, Roses grow best in the ground but should do OK in a 15 gallon pot in your area.
Roses as with most plants are limited to how big they get by the root system. They will attempt to grow larger but this growth can be stunted if placed in too small of a pot.
Knock Out wants to be a large shrub but Roses are one plant than can be kept smaller by pruning. Because roses, especially Knock Out, bloom in flushes, rest a little, then produce another flush of bloom, removing spent bloom and shaping it with a pair of hedge trimmers, reducing it's size as you do, will keep it in bounds.
Potted plants of any kind need to be watered often. The soil should not be allowed to dry out completely. This is not saying the soil should be wet, more like moist as in a wrung out sponge. You should have drain holes in the bottom of the pot and water until it runs from the bottom.
In hot dry weather, a daily watering is not too much. Do
not set the pot in a tray or shallow dish that will hold water. Roots kept constantly wet can rot and the soil can sour due to lack of air.
Use a good potting soil, not soil from your garden which can be quite heavy. Fertilize often with half strength fertilizers and occassionally add some organics to the pot to keep the soil healthy and loose.
While water running through the pot keeps salts from building up, it also leaches out the minerals over time. Therefore a well balanced fetilizer with micro nutrients should be used at half strength often. A little fertilizer, often, is better than a lot all at once.
It keeps growth more even and avoids quick growth spurts.
While many areas in Tennesse can get quite cold especially in the nortern portion of the state, for the most part your potted rose should do well with little or no winter protection.
If concerned, place it on a pot dolly so you can roll it into an unheated garage or shed during bitter cold periods.
During visits to your state for Rose Conventions, I saw lots of rose enthusiasts growing roses in pots. If I knew better the area you live I could refer you to rose societies, consulting rosarians, or nurseries such as Rosemania. Ann Peck near Knoxville grows many roses and there are others near Nashville and Memphis.
Chose healthy plants from reputible garden centers or nurseries.