I just checked the RV NET FORUM a few minutes ago (9AM) after reading your post using GOOGLE CHROME BROWSER and all looks good here at this time. I too have seen the Site Security Certificate notification only on the RV NET FORUM.
Like many other I have quit using the RV NET FOURM for over a year now since it seems to keep having problems.
I can get to the RV NET FORUM though several RV NET FORUM PORTALS which for some reason seem to get around all of these problem.
I use WOODALLs and sometimes TRAILERLIFE PORTALS to get to the RV.NET forum using my same login password and user name. The WOODALLs portal access for me seems to have less advertisements associated with it... I for the most part use FIREFOX as my browser but since I am running dual 24-inch monitors I here lately have been running GOOGLE CHROME on Monitor One and FIREFOX on Monitor Two.. I have a whole group of Internet Radio Scanners tabs (7 or 8) all listed on my Monitor One and they all seem to work better using Google Chrome's ADOBE FLASH...
I still get to see all of the posts and features of the RV.NET...
This particular SITE SECURITY CERTIFICATE notification has been on-going for a couple of weeks now... Here at this location it comes and goes...
Lots of info posted on this subj on the Forum Technical Support thread
Roy Ken