Arguably this type of employment is a "travelling appointment" and subsistence would be claimable.
See Section 4.3 in Revenue's TDM 05-01-06 "Tax treatment of the reimbursement of expenses of
travel and subsistence to office holders and employees"
4.3 ‘Travelling appointments’
A ‘travelling appointment’ is one where either:
a) an employee is required to travel in the course of her/his job (for example, an
occupation which generally involves multiple daily appointments with
customers (e.g. travelling salesperson, travelling repair person, service
engineers, etc.-); or
b) travelling is an integral part of the job (for example, bus driver, lorry driver,
coach driver, or van driver etc.).
The reimbursement of expenses by the employer to such an employee is generally
only in relation to subsistence but may sometimes include expenses of travelling
where an office holder or employee is required to use her/his own car on a business
journey.
Where an individual whose job can be categorised as a ‘travelling appointment’
would not otherwise be regarded as having a ‘normal place of work’ for the purposes
of computing travel and subsistence expenses for this category of worker, her/his
employer’s base will be regarded as her/his normal place of work.
Where a business journey commences from the employee’s home or the employee
returns directly to home, then the expenses of travel and subsistence that may be
reimbursed without deduction of tax are the lesser of those incurred on the journey
between:
a) home and the temporary work location; or
b) the employer’s base (normal place of work) and the temporary work location.