The only 'caulking' that was used by Airstream on roof A/C units was to seal their proprietary drain pan to the roof. No other sealants were used in the mounting process.
No other RV manufacturer: (1) uses a plastic drain pan and (2) does not use ANY sealant to secure a roof A/C unit to the roof.
Newer model Airstreams have in fact done away with this problem prone drain pan and have started using Dometic's Auxiliary Drain Kit #3107688.016. The roof unit is clamped to the roof using a pair of stacked 1" thick rubberized foam sealing gaskets that are then compressed to 50% of their original thickness when the mounting bolts from the bottom flange are properly tightened.
The only 'sealant' used in this application is to close the channels cut into the upper gasket to allow the drain hose to pass thru.