Semiconductor switching of course is best solution but has its own problems with heat output and is not something that can be added to correct the problem with the thermostat they already have.
Usually arcing occurs when the contacts are broken so that would be good info to know. If it trips during release (when the power is turned off to the heat).
Your link to line filters is for components and not a plug in solution. I was thinking more towards line conditioners that would be a plug in solution and may have built in line filters and such.