What sealant for cockpit floor panel?

[boden36]

I am about to refit a steel panel to Nekeyah's cockpit floor. It is about 3 ft by 2'6" and is bolted down about every 4'.
The panel is gasketed by 1/8" insertion rubber.
In the past I have used a sealant called Butyl Mastic but find that it dries out after a while.
Any suggestions for a sealant that will skin but not set in this application?
(Preferably something that may be available in Australia)

Regards,

Richard.