Well, to Shortbus's comment about having to push RTV, I've used pourable types of RTV in the distant past.

For what?

He could buy the real conformal coating for that price.

 

For what?

That has to have been a good 20 years ago. Was working for a company that made "Down Hole Measurement Tools" for off-shore oil rigs. Down at the bottom of a well being drilled is very high shock and vibration. Simply CC'ing a board would not help. Taking the time to pot every component was time consuming. They made a mold they could pour the RTV into then set the board - component side down - into the RTV. It was the second to the last thing that was done to the board. The last thing was to close up its module before stuffing it into a pressure housing.

They had a bunch of expired tubes of the stuff they wanted to get rid of. So I asked if I could take some tubes home. They had no problem with it. I had an aluminum dished light fixture and modified it to act as a shotgun microphone. Because the dish would ring at certain frequencies I coated it with a couple layers of the stuff on the back side to muffle any ringing. Ringing like when you tap a glass with a spoon. So I have used the stuff, but that was before the divorce where the wife got everything. Including all my tools and electronics stockpile. Back then I had a pretty impressive cache. There were frequent times when they would purge stock of stuff they no longer wanted to use. I must have had a couple hundred photo-transistors, a dozen pump stroke counters (electronic counters that counted switch closings), many many IC's, logic gates and stuff. Had a chart recorder, dumb computer monitor and a ball printer. Many other things too. All gone with the bitc---- never mind.

 

@pager48 None of us here think you need to epoxy the board. A simple coating should suffice. Conformal coating by the spray can is not very cheap. You could spend around $20 to $30 for a can, but you can coat a lot of boards with that one can.

Back when my interest in electronics was burgeoning I built an amplifier for my telephone. Didn't NEED to, but I wanted to. I have no idea why I did this but I melted candle wax and coated the entire board with it. Since it was in a phone in the house it wasn't going to melt. Maybe wax is a dumb idea; but it was readily available and cheap. And I don't think anything could get to the board in the way of moisture or foreign objects.