Spray silicone isn't going to hurt it, I'd get some silicone plumber's grease to do a better job of sealing the gasket.
Often black tank odors get into the bathroom due to the toilet valve not being totally closed. I always fill the bowl with a half inch of water after flushing. If the water drains out, I know the valve isn't sealing properly. Another issue is traveling with windows or roof vents open. The low pressure crated in the RV will draw odors in from the black tank.
Bob & Donna
'98 Gulf Stream Sun Voyager DP being pushed by a '00 Beetle TDI