I would contact your local building inspection department to find out what landlord responsibilities are with respect to setting homes on your lots. Local governments, in most states, have established regulations which require the landlord to provide certain facilities to each lot. e.g. sewer connections, water, electrical, telephone and cable access. Some may require all these facilities, others less. In our locality, the set up of any MH is the responsibility of the tenant, with the landlord's input as to exact positioning of the home on the lot.
Normally, the set up, and cost of same, are bundled into the sale price of the MH when purchased from the MH dealer. Check with the new tenant and see if their bill of sale included on site set up charges. If the MH dealer did not include these concrete footer costs in the sale price, and your local regulations do not require the landlord to provide them, then it should be up to the tenant.
These are my opinions only, and you should rely on your own research to understand your obligations in this situation.