I think that more typically, they use the "butyl tape" to seal that vent cover, but I was told by a tech from Suburban that you can use any caulk. He assured me that it won't get too hot in that spot, even w/ the furnace running. So I put a bead of vulkem around it the last time I had it off the trailer (had to remove the furnace to access/replace the bad thermocouple). haven't had any problem with the vent or its caulking, although I don't use it much.
'73 Safari 23'
'00 Dodge Ram 1500 4x4 QC