If the gp24/27/29 "DC" series batteries are like the Costco/Interstate versions, which is very likely, they say on them that they are deep cycle batteries. In reality, that probably aren't in the sense that we have usually thought of that term. They may or may not have internal things to help with cycle life and depth of discharge handling, but hard to confirm that. They do have water checking and adding caps which normally would indicate that they would be traditional deep cycle chemistry which needs water additions.
I have had a couple of the DC series from Costco that I use for the starting battery in or Chevy Roadtrek 190. We had a gp27 first and now gp24 as it is easier to get in and out than the gp27 which was very tight and difficult. They are good batteries and last pretty well, but they don't behave like deep cycle batteries do to a large extent. The most obvious thing is that they don't really use any water, even on the charger for long float periods. I have had them on over an entire winter without having to add water. This would indicate a low water use design like is used in all the sealed starting and combo batteries, not deep cycle. They also don't come up to as high a voltage as the deep cycles we have had which would also. Both didn't really come up more than to about 12.6v except for when they had a bit of surface charge. Specific gravity readings were also lower at about 1260-1265 on the high end.
For those that are locked into those case sizes, they are probably among the better choices, but probably closer to a marine starting battery than a true deep cycle one. I think you can still get a true deep cycle 12v from Trojan and Crown, but not sure on that. Equipment batteries from them like for floor scrubbers are said to be quite good. IIRC, the Trojan one was 24MTX and was said to be a very good battery. We had a couple of the SCS series which had more output, but according to the old school dealear they weren't as durable, which is what we found also. The SCS batteries where decent but nowhere near what the later installed Trojan GC 6 volt ones were. They tested as new after 5 years of testing and abuse as we worked on various system configurations.