Hello
You might want to look into ordinary foam that is used to seal household air leaks..Rigid foam is very low cost and
has a low dielectric constant..This keeps stray capacities as low as possible(air being the lowest)..
This may not be as important in your particular circuit but in some cases strays can cause peculiar glitches.
Just dont use too much foam so that you over compress the circuit..practice, practice, practice before committing your device as others have said can be very hard to undo and or you may lose it.
Goodluck