Proflex RV is a good sealant. Geocel also offers different sealants for truck/trailer and OEM builders. You could check with them about your particular use and see if one is better than another.
FWIW, when I was sealing my trailer, I used Geocel 2300 Construction adhesive. It's specs were just a tad better than Proflex and is also a tri polymer adhesive/sealant. Specs change as do formulations so if the job is important, I'd give them a call.