The first picture shows a stress crack in the fiberglass. There may be some delamination in that area, depicting water under the fiberglass.
The second picture shows a piece of something holding the slide seal open at that point. Don't know if that is a diverter or a loose piece of plastic trim from the slide but I wouldn't want it there.
Third picture is a separation in the trim-> siding. The caulk depicted looks a lot like old siliconized latex caulk, typical home-owner stuff. It will need to be removed, totally, and new sealant like Geocel Proflex RV put into the joint. All traces of any silicone caulk need to be removed prior to resealing. Mineral spirits helps with a final clean up.
The last picture shows the same type of bad sealing. Looks like multiple types of caulk applied because the initial sealing didn't go right. Procedure is the same as #3 situation.
I would suggest that you go over all joints in the trailer and remove the poor sealing efforts and reapply a good caulk. After that, I'd suggest to do a pressurized leak test. You can DIY the pressure test. Sealtech is a commercial pressure testing system and is available through RV dealers.
