RTV ageing?

We have an application where to protect pressure sensor it has been proposed
that RTV-485 be placed on the face of the sensor to afford additional
protection against the water (rivers/sewage/estuaries/floodways etc) in
which it is placed. The sensors are quite sensitive and measure depths up
to ~ 5m. The sensor face is about 10mm in diameter and is already protected
by a very soft gel. The coating applied would be 1 - 2mm thick.
I have concerns that:
1) As the RTV cures and/or ages it will shrink pre-loading the face of the
sensor causing an offset.
2) As the RTV ages or absorbs water its flexibility will change causing
pressure "gain" or linearity errors.
Any advice greatly appreciated.
rob