Hyperthermal atoms may be implanted beneath single layers of graphene or hexagonal boron nitride (h-BN) on a substrate. For the case of h-BN on rhodium, which is a corrugated honeycomb superstructure with a periodicity of 3.2 nm, Ar atoms are implanted at distinct interstitial sites within the supercell, where the h-BN is weakly bound to the substrate. These peculiar structures are reminiscent of "nanotents" with an ultimately thin "rainfly". Here we explore the implantation length (i.e., the distance the atoms move before they come to rest as interstitial defects) and the thermal stability of these atomic agglomerates above room temperature. The results are obtained by variable-temperature scanning tunneling microscopy and density functional theory calculations.