Hi,
You did not specify the model and year of your Sunline, nor the tire size. We can verify that the tire size, load range, and type (specifically ST trailer tires for your camper size) are correct, which is the most critical aspect. Sometimes, prior owners install tires with a load range that is less than the correct one for several reasons; thus, this needs to be checked when you add new tires.
As for brands, everyone has their preferences or a brand they trust, as they know a local tire dealer who suggested that brand. Again, ensuring they are the correct size, load range, and ST trailer tires, and that they are inflated to the maximum cold sidewall pressure before each camping trip, is crucial.
Here are my three picks for brands from my experience on the trailers I use ST trailer tires for.
Not in any order of which is best, all three are good. However, they must be from this brand or category within those brands. I have used the CarlStar on my smaller campers and flat bed trailer with no issues. Any of these brands should be changed after 5 years of use due to rubber breakdown, regardless of tread life. Most trailer tires age out before they wear out. Trailer tires differ significantly from automobile tires.
1. Goodyear - Endurance, if they offer your size.
https://www.goodyear.com/en_US/tires/endurance-trailer-tire/24464.html
2. Maxxis - M8008 Plus ST Radial
M8008 Plus ST RADIAL
3. Carlstar - Radial Trail HD
https://www.carlstar.com/our-products/product-detail/radial-trail-hd/
Discount Tire in our area has good deals on all of them. Ensure you request high-pressure snap-in valve stems. They have the rubber boot at the rim and a brass stem. They usually do not cost any more, but are a better valve stem. With so many cheap, inferior valve stems available nowadays, it pays to ensure you get the better ones.
If you request that the tire manufacturer's dates be within one year of the time they install, they most of the time will try to accommodate, but only if you ask. Just have the time and tell them you can wait a week or so for the best outcome. They may have to search for the dates, and the warehouse folks get a bit annoyed sometimes. There is no requirement that you cannot sell a 3 or 4-year-old tire as new. That only leaves you with less time before the 5-year change-out mark.
I hope this helps.
John
P.S., On my larger camper, a 2004 T310SR, I have converted to LT truck tires due to the weight and size, but that is a very different situation than your camper size.