I bought WMR200 few weeks ago. Installed on the roof, set up WeeWX software on dedicated Raspberry Pi. Signal outages, null values in database were frequent. First antenna mod was paper clip - didn't work for me. Relocating station helped a little.
Second antenna mod. I bought a 433 MHz antenna (for motorized gateways) with 6 meters of RG-58 cable. I had to remove old antenna from the station and install a SMA connector (easy, and didn't break the screen). The new external antenna has been installed on the roof. Signal outages were less frequent. What to do?
I decided that it will be better to copy last value (from previous good reading) instead of inserting NULL into the database (I'm logging to MySQL). So I prepared a MySQL trigger which does this. First of all it selects last value of out temperature, wind, humidity and so on. Next it checks if new value is null. If it is the last value is inserted instead. Finally the incident of sensor outage is logged into another table.
If you will be interested I will paste code of the trigger.