Best sealant for external joints - what do the pros use?

I'm going to reseal all the external joints on our caravan this summer as preventative maintenance. What sealant do the professionals actually use? I want to do this properly - buy the right stuff once rather than cheap out and regret it.

Sikaflex 512 all the way. It's what most caravan service engineers use. It's a polyurethane sealant that bonds incredibly well to caravan panels, stays flexible so it won't crack with the expansion and contraction you get through the seasons, and it's UV resistant. Costs about £12 a tube but it's worth every penny. Also invest in a proper sealant smoothing tool - makes the finish look professional.