To the very best of my knowledge they do nothing.....
The idea behind their thinking (NOTE, Express Vu thinking NOT mine) is that if the Dish is pointed correctly, the signal will be strong enough for most cases of Heavy Rain etc.
In the real world I find it pretty ironic that Commercial Installations for say Banks etc are all done with 60cm (24") Dish's. Now why would you do this for Commercial and not make it available to Residential, I do not know.
I can only think that firstly, ensure the Dish is perfectly aligned, Record Signal Strengths on a clear day, then call Express Vu when you loose signal due to Rain.
Adding an In-Line Amp will not really help unless the cable run is very long, over 200 - 250 feet. I have one line in my house that is 375 feet in length, it was never an issue, it lost signal almost the same as the others. Levels were only 5% down on the 125 foot runs.
It could be that the LNBF is not working fully.
Could be a loose or slightly corroded Connector, allowing for voltage drop.
Try the obvious first, connectors, LNBF's, pointing etc, if none of that works then you really do need a bigger Dish or at the very least another Dish.
It will not surprise you to know that during an experiment I did 2 years ago, I assembled 6 x 51cm (20") Dish's, mounted and peaked them on the same Mount and got 6 Different Signal Levels.
Repeated the experiment with 6 Mounts on the same exterior Wall and had techs peak them, same result. One Dish would not climb above 89% T11 Nimiq 1, whilst another hit 100% and would have continued higher if there was room on the screen.....
ALL Dish's are NOT created equal.
I have even seen Dish's that WILL NOT receive any Signal at all......
There is, to the best of my knowledge no way you can even buy a Dish from Express Vu. you have to get through to a Level 3 Tech Support Person and then and only then you might get one shipped out for $75 or $99, it seems to vary.