Im a little unsure why a deep meson site is a better option than a very big SDB - the size of the caverns needed for the Deep Meson Site should show up on gravity and other sensors, as should much of the support equipment, and the sensor systems feeding them
data are still vulnerable to orbital bombardment even if the site isnt. Im not even get to the need for radiators for the power requirement for them.
Basically, IMO a buffered plantoid in orbit with really thick armor gets you most of the advantages of the deep meson site, and the tunnelling should be simpler, and with Trav technology you can move it at one gee.