I would suggest you plan on a day for getting all over your rig and sealing everything. The roof through-holes for vents, AC's, etc. is one area. Around any siding and trim is also important. If the windows aren't leaking, as long as you have caulk gun in hand, go around the perimeter of the window after you have carved out the squeezed butyl tape. There is no sense to seal failing material, IMO, and any cracked or loose sealants should be removed first.
I use a lot of different caulks and sealants in my occupation and found that the Geocel products like Proflex RV is an excellent sealant for my trailer. I am currently using Geocel Tripolymer 2300. It has a slightly better elongation rating than Proflex but not much. Geocel is now making another sealant that is for the trailer and mobile industry, 2300 MHRV, which has an even higher elongation rating. I may try that next.